diff --git a/generators/dart/colour.js b/generators/dart/colour.js
index 2f1adcbcd..e19202928 100644
--- a/generators/dart/colour.js
+++ b/generators/dart/colour.js
@@ -18,7 +18,7 @@ Blockly.Dart.addReservedWords('Math');
 
 Blockly.Dart['colour_picker'] = function(block) {
   // Colour picker.
-  var code = Blockly.Dart.quote_(block.getFieldValue('COLOUR'));
+  const code = Blockly.Dart.quote_(block.getFieldValue('COLOUR'));
   return [code, Blockly.Dart.ORDER_ATOMIC];
 };
 
@@ -26,7 +26,7 @@ Blockly.Dart['colour_random'] = function(block) {
   // Generate a random colour.
   Blockly.Dart.definitions_['import_dart_math'] =
       'import \'dart:math\' as Math;';
-  var functionName = Blockly.Dart.provideFunction_(
+  const functionName = Blockly.Dart.provideFunction_(
       'colour_random',
       ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ + '() {',
        '  String hex = \'0123456789abcdef\';',
@@ -35,22 +35,22 @@ Blockly.Dart['colour_random'] = function(block) {
        '      \'${hex[rnd.nextInt(16)]}${hex[rnd.nextInt(16)]}\'',
        '      \'${hex[rnd.nextInt(16)]}${hex[rnd.nextInt(16)]}\';',
        '}']);
-  var code = functionName + '()';
+  const code = functionName + '()';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['colour_rgb'] = function(block) {
   // Compose a colour from RGB components expressed as percentages.
-  var red = Blockly.Dart.valueToCode(block, 'RED',
+  const red = Blockly.Dart.valueToCode(block, 'RED',
       Blockly.Dart.ORDER_NONE) || 0;
-  var green = Blockly.Dart.valueToCode(block, 'GREEN',
+  const green = Blockly.Dart.valueToCode(block, 'GREEN',
       Blockly.Dart.ORDER_NONE) || 0;
-  var blue = Blockly.Dart.valueToCode(block, 'BLUE',
+  const blue = Blockly.Dart.valueToCode(block, 'BLUE',
       Blockly.Dart.ORDER_NONE) || 0;
 
   Blockly.Dart.definitions_['import_dart_math'] =
       'import \'dart:math\' as Math;';
-  var functionName = Blockly.Dart.provideFunction_(
+  const functionName = Blockly.Dart.provideFunction_(
       'colour_rgb',
       ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
           '(num r, num g, num b) {',
@@ -68,22 +68,22 @@ Blockly.Dart['colour_rgb'] = function(block) {
        '  bs = bs.substring(bs.length - 2);',
        '  return \'#$rs$gs$bs\';',
        '}']);
-  var code = functionName + '(' + red + ', ' + green + ', ' + blue + ')';
+  const code = functionName + '(' + red + ', ' + green + ', ' + blue + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['colour_blend'] = function(block) {
   // Blend two colours together.
-  var c1 = Blockly.Dart.valueToCode(block, 'COLOUR1',
+  const c1 = Blockly.Dart.valueToCode(block, 'COLOUR1',
       Blockly.Dart.ORDER_NONE) || '\'#000000\'';
-  var c2 = Blockly.Dart.valueToCode(block, 'COLOUR2',
+  const c2 = Blockly.Dart.valueToCode(block, 'COLOUR2',
       Blockly.Dart.ORDER_NONE) || '\'#000000\'';
-  var ratio = Blockly.Dart.valueToCode(block, 'RATIO',
+  const ratio = Blockly.Dart.valueToCode(block, 'RATIO',
       Blockly.Dart.ORDER_NONE) || 0.5;
 
   Blockly.Dart.definitions_['import_dart_math'] =
       'import \'dart:math\' as Math;';
-  var functionName = Blockly.Dart.provideFunction_(
+  const functionName = Blockly.Dart.provideFunction_(
       'colour_blend',
       ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
           '(String c1, String c2, num ratio) {',
@@ -108,6 +108,6 @@ Blockly.Dart['colour_blend'] = function(block) {
        '  bs = bs.substring(bs.length - 2);',
        '  return \'#$rs$gs$bs\';',
        '}']);
-  var code = functionName + '(' + c1 + ', ' + c2 + ', ' + ratio + ')';
+  const code = functionName + '(' + c1 + ', ' + c2 + ', ' + ratio + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
diff --git a/generators/dart/lists.js b/generators/dart/lists.js
index f0af7a34c..05419a54b 100644
--- a/generators/dart/lists.js
+++ b/generators/dart/lists.js
@@ -23,48 +23,48 @@ Blockly.Dart['lists_create_empty'] = function(block) {
 
 Blockly.Dart['lists_create_with'] = function(block) {
   // Create a list with any number of elements of any type.
-  var elements = new Array(block.itemCount_);
-  for (var i = 0; i < block.itemCount_; i++) {
+  const elements = new Array(block.itemCount_);
+  for (let i = 0; i < block.itemCount_; i++) {
     elements[i] = Blockly.Dart.valueToCode(block, 'ADD' + i,
         Blockly.Dart.ORDER_NONE) || 'null';
   }
-  var code = '[' + elements.join(', ') + ']';
+  const code = '[' + elements.join(', ') + ']';
   return [code, Blockly.Dart.ORDER_ATOMIC];
 };
 
 Blockly.Dart['lists_repeat'] = function(block) {
   // Create a list with one element repeated.
-  var element = Blockly.Dart.valueToCode(block, 'ITEM',
+  const element = Blockly.Dart.valueToCode(block, 'ITEM',
       Blockly.Dart.ORDER_NONE) || 'null';
-  var repeatCount = Blockly.Dart.valueToCode(block, 'NUM',
+  const repeatCount = Blockly.Dart.valueToCode(block, 'NUM',
       Blockly.Dart.ORDER_NONE) || '0';
-  var code = 'new List.filled(' + repeatCount + ', ' + element + ')';
+  const code = 'new List.filled(' + repeatCount + ', ' + element + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['lists_length'] = function(block) {
   // String or array length.
-  var list = Blockly.Dart.valueToCode(block, 'VALUE',
+  const list = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '[]';
   return [list + '.length', Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['lists_isEmpty'] = function(block) {
   // Is the string null or array empty?
-  var list = Blockly.Dart.valueToCode(block, 'VALUE',
+  const list = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '[]';
   return [list + '.isEmpty', Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['lists_indexOf'] = function(block) {
   // Find an item in the list.
-  var operator = block.getFieldValue('END') === 'FIRST' ?
+  const operator = block.getFieldValue('END') === 'FIRST' ?
       'indexOf' : 'lastIndexOf';
-  var item = Blockly.Dart.valueToCode(block, 'FIND',
+  const item = Blockly.Dart.valueToCode(block, 'FIND',
       Blockly.Dart.ORDER_NONE) || '\'\'';
-  var list = Blockly.Dart.valueToCode(block, 'VALUE',
+  const list = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '[]';
-  var code = list + '.' + operator + '(' + item + ')';
+  const code = list + '.' + operator + '(' + item + ')';
   if (block.workspace.options.oneBasedIndex) {
     return [code + ' + 1', Blockly.Dart.ORDER_ADDITIVE];
   }
@@ -74,17 +74,17 @@ Blockly.Dart['lists_indexOf'] = function(block) {
 Blockly.Dart['lists_getIndex'] = function(block) {
   // Get element at index.
   // Note: Until January 2013 this block did not have MODE or WHERE inputs.
-  var mode = block.getFieldValue('MODE') || 'GET';
-  var where = block.getFieldValue('WHERE') || 'FROM_START';
-  var listOrder = (where === 'RANDOM' || where === 'FROM_END') ?
+  const mode = block.getFieldValue('MODE') || 'GET';
+  const where = block.getFieldValue('WHERE') || 'FROM_START';
+  const listOrder = (where === 'RANDOM' || where === 'FROM_END') ?
       Blockly.Dart.ORDER_NONE : Blockly.Dart.ORDER_UNARY_POSTFIX;
-  var list = Blockly.Dart.valueToCode(block, 'VALUE', listOrder) || '[]';
+  let list = Blockly.Dart.valueToCode(block, 'VALUE', listOrder) || '[]';
   // Cache non-trivial values to variables to prevent repeated look-ups.
   // Closure, which accesses and modifies 'list'.
   function cacheList() {
-    var listVar = Blockly.Dart.nameDB_.getDistinctName(
+    const listVar = Blockly.Dart.nameDB_.getDistinctName(
         'tmp_list', Blockly.VARIABLE_CATEGORY_NAME);
-    var code = 'List ' + listVar + ' = ' + list + ';\n';
+    const code = 'List ' + listVar + ' = ' + list + ';\n';
     list = listVar;
     return code;
   }
@@ -98,8 +98,8 @@ Blockly.Dart['lists_getIndex'] = function(block) {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
       // We can use multiple statements.
-      var code = cacheList();
-      var xVar = Blockly.Dart.nameDB_.getDistinctName(
+      let code = cacheList();
+      const xVar = Blockly.Dart.nameDB_.getDistinctName(
           'tmp_x', Blockly.VARIABLE_CATEGORY_NAME);
       code += 'int ' + xVar + ' = new Math.Random().nextInt(' + list +
           '.length);\n';
@@ -108,35 +108,35 @@ Blockly.Dart['lists_getIndex'] = function(block) {
     } else {  // where === 'FROM_END'
       if (mode === 'REMOVE') {
         // We can use multiple statements.
-        var at = Blockly.Dart.getAdjusted(block, 'AT', 1, false,
+        const at = Blockly.Dart.getAdjusted(block, 'AT', 1, false,
             Blockly.Dart.ORDER_ADDITIVE);
-        var code = cacheList();
+        let code = cacheList();
         code += list + '.removeAt(' + list + '.length' + ' - ' + at + ');\n';
         return code;
 
       } else if (mode === 'GET') {
-        var at = Blockly.Dart.getAdjusted(block, 'AT', 1);
+        const at = Blockly.Dart.getAdjusted(block, 'AT', 1);
         // We need to create a procedure to avoid reevaluating values.
-        var functionName = Blockly.Dart.provideFunction_(
+        const functionName = Blockly.Dart.provideFunction_(
             'lists_get_from_end',
             ['dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
             '(List my_list, num x) {',
               '  x = my_list.length - x;',
               '  return my_list[x];',
               '}']);
-        var code = functionName + '(' + list + ', ' + at + ')';
+        const code = functionName + '(' + list + ', ' + at + ')';
         return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
       } else if (mode === 'GET_REMOVE') {
-        var at = Blockly.Dart.getAdjusted(block, 'AT', 1);
+        const at = Blockly.Dart.getAdjusted(block, 'AT', 1);
         // We need to create a procedure to avoid reevaluating values.
-        var functionName = Blockly.Dart.provideFunction_(
+        const functionName = Blockly.Dart.provideFunction_(
             'lists_remove_from_end',
             ['dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
             '(List my_list, num x) {',
               '  x = my_list.length - x;',
               '  return my_list.removeAt(x);',
               '}']);
-        var code = functionName + '(' + list + ', ' + at + ')';
+        const code = functionName + '(' + list + ', ' + at + ')';
         return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
       }
     }
@@ -146,10 +146,10 @@ Blockly.Dart['lists_getIndex'] = function(block) {
     switch (where) {
       case 'FIRST':
         if (mode === 'GET') {
-          var code = list + '.first';
+          const code = list + '.first';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'GET_REMOVE') {
-          var code = list + '.removeAt(0)';
+          const code = list + '.removeAt(0)';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'REMOVE') {
           return list + '.removeAt(0);\n';
@@ -157,35 +157,36 @@ Blockly.Dart['lists_getIndex'] = function(block) {
         break;
       case 'LAST':
         if (mode === 'GET') {
-          var code = list + '.last';
+          const code = list + '.last';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'GET_REMOVE') {
-          var code = list + '.removeLast()';
+          const code = list + '.removeLast()';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'REMOVE') {
           return list + '.removeLast();\n';
         }
         break;
-      case 'FROM_START':
-        var at = Blockly.Dart.getAdjusted(block, 'AT');
+      case 'FROM_START': {
+        const at = Blockly.Dart.getAdjusted(block, 'AT');
         if (mode === 'GET') {
-          var code = list + '[' + at + ']';
+          const code = list + '[' + at + ']';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'GET_REMOVE') {
-          var code = list + '.removeAt(' + at + ')';
+          const code = list + '.removeAt(' + at + ')';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'REMOVE') {
           return list + '.removeAt(' + at + ');\n';
         }
         break;
-      case 'FROM_END':
-        var at = Blockly.Dart.getAdjusted(block, 'AT', 1, false,
+      }
+      case 'FROM_END': {
+        const at = Blockly.Dart.getAdjusted(block, 'AT', 1, false,
             Blockly.Dart.ORDER_ADDITIVE);
         if (mode === 'GET') {
-          var code = list + '[' + list + '.length - ' + at + ']';
+          const code = list + '[' + list + '.length - ' + at + ']';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'GET_REMOVE' || mode === 'REMOVE') {
-          var code = list + '.removeAt(' + list + '.length - ' + at + ')';
+          const code = list + '.removeAt(' + list + '.length - ' + at + ')';
           if (mode === 'GET_REMOVE') {
             return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
           } else if (mode === 'REMOVE') {
@@ -193,36 +194,37 @@ Blockly.Dart['lists_getIndex'] = function(block) {
           }
         }
         break;
+      }
       case 'RANDOM':
         Blockly.Dart.definitions_['import_dart_math'] =
             'import \'dart:math\' as Math;';
         if (mode === 'REMOVE') {
           // We can use multiple statements.
-          var xVar = Blockly.Dart.nameDB_.getDistinctName(
+          const xVar = Blockly.Dart.nameDB_.getDistinctName(
               'tmp_x', Blockly.VARIABLE_CATEGORY_NAME);
-          var code = 'int ' + xVar + ' = new Math.Random().nextInt(' + list +
+          let code = 'int ' + xVar + ' = new Math.Random().nextInt(' + list +
               '.length);\n';
           code += list + '.removeAt(' + xVar + ');\n';
           return code;
         } else if (mode === 'GET') {
-          var functionName = Blockly.Dart.provideFunction_(
-              'lists_get_random_item',
-              ['dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
-              '(List my_list) {',
+          const functionName =
+              Blockly.Dart.provideFunction_('lists_get_random_item', [
+                'dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
+                    '(List my_list) {',
                 '  int x = new Math.Random().nextInt(my_list.length);',
-                '  return my_list[x];',
-                '}']);
-          var code = functionName + '(' + list + ')';
+                '  return my_list[x];', '}'
+              ]);
+          const code = functionName + '(' + list + ')';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         } else if (mode === 'GET_REMOVE') {
-          var functionName = Blockly.Dart.provideFunction_(
-              'lists_remove_random_item',
-              ['dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
-              '(List my_list) {',
+          const functionName =
+              Blockly.Dart.provideFunction_('lists_remove_random_item', [
+                'dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
+                    '(List my_list) {',
                 '  int x = new Math.Random().nextInt(my_list.length);',
-                '  return my_list.removeAt(x);',
-                '}']);
-          var code = functionName + '(' + list + ')';
+                '  return my_list.removeAt(x);', '}'
+              ]);
+          const code = functionName + '(' + list + ')';
           return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
         }
         break;
@@ -234,11 +236,11 @@ Blockly.Dart['lists_getIndex'] = function(block) {
 Blockly.Dart['lists_setIndex'] = function(block) {
   // Set element at index.
   // Note: Until February 2013 this block did not have MODE or WHERE inputs.
-  var mode = block.getFieldValue('MODE') || 'GET';
-  var where = block.getFieldValue('WHERE') || 'FROM_START';
-  var list = Blockly.Dart.valueToCode(block, 'LIST',
+  const mode = block.getFieldValue('MODE') || 'GET';
+  const where = block.getFieldValue('WHERE') || 'FROM_START';
+  let list = Blockly.Dart.valueToCode(block, 'LIST',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '[]';
-  var value = Blockly.Dart.valueToCode(block, 'TO',
+  const value = Blockly.Dart.valueToCode(block, 'TO',
       Blockly.Dart.ORDER_ASSIGNMENT) || 'null';
   // Cache non-trivial values to variables to prevent repeated look-ups.
   // Closure, which accesses and modifies 'list'.
@@ -246,9 +248,9 @@ Blockly.Dart['lists_setIndex'] = function(block) {
     if (list.match(/^\w+$/)) {
       return '';
     }
-    var listVar = Blockly.Dart.nameDB_.getDistinctName(
+    const listVar = Blockly.Dart.nameDB_.getDistinctName(
         'tmp_list', Blockly.VARIABLE_CATEGORY_NAME);
-    var code = 'List ' + listVar + ' = ' + list + ';\n';
+    const code = 'List ' + listVar + ' = ' + list + ';\n';
     list = listVar;
     return code;
   }
@@ -262,25 +264,26 @@ Blockly.Dart['lists_setIndex'] = function(block) {
       break;
     case 'LAST':
       if (mode === 'SET') {
-        var code = cacheList();
+        let code = cacheList();
         code += list + '[' + list + '.length - 1] = ' + value + ';\n';
         return code;
       } else if (mode === 'INSERT') {
         return list + '.add(' + value + ');\n';
       }
       break;
-    case 'FROM_START':
-      var at = Blockly.Dart.getAdjusted(block, 'AT');
+    case 'FROM_START': {
+      const at = Blockly.Dart.getAdjusted(block, 'AT');
       if (mode === 'SET') {
         return list + '[' + at + '] = ' + value + ';\n';
       } else if (mode === 'INSERT') {
         return list + '.insert(' + at + ', ' + value + ');\n';
       }
       break;
-    case 'FROM_END':
-      var at = Blockly.Dart.getAdjusted(block, 'AT', 1, false,
-          Blockly.Dart.ORDER_ADDITIVE);
-      var code = cacheList();
+    }
+    case 'FROM_END': {
+      const at = Blockly.Dart.getAdjusted(
+          block, 'AT', 1, false, Blockly.Dart.ORDER_ADDITIVE);
+      let code = cacheList();
       if (mode === 'SET') {
         code += list + '[' + list + '.length - ' + at + '] = ' + value +
             ';\n';
@@ -291,11 +294,12 @@ Blockly.Dart['lists_setIndex'] = function(block) {
         return code;
       }
       break;
-    case 'RANDOM':
+    }
+    case 'RANDOM': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
-      var code = cacheList();
-      var xVar = Blockly.Dart.nameDB_.getDistinctName(
+      let code = cacheList();
+      const xVar = Blockly.Dart.nameDB_.getDistinctName(
           'tmp_x', Blockly.VARIABLE_CATEGORY_NAME);
       code += 'int ' + xVar +
           ' = new Math.Random().nextInt(' + list + '.length);\n';
@@ -307,40 +311,44 @@ Blockly.Dart['lists_setIndex'] = function(block) {
         return code;
       }
       break;
+    }
   }
   throw Error('Unhandled combination (lists_setIndex).');
 };
 
 Blockly.Dart['lists_getSublist'] = function(block) {
   // Get sublist.
-  var list = Blockly.Dart.valueToCode(block, 'LIST',
+  const list = Blockly.Dart.valueToCode(block, 'LIST',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '[]';
-  var where1 = block.getFieldValue('WHERE1');
-  var where2 = block.getFieldValue('WHERE2');
+  const where1 = block.getFieldValue('WHERE1');
+  const where2 = block.getFieldValue('WHERE2');
+  let code;
   if (list.match(/^\w+$/) || (where1 !== 'FROM_END' && where2 === 'FROM_START')) {
     // If the list is a is a variable or doesn't require a call for length,
     // don't generate a helper function.
+    let at1;
     switch (where1) {
       case 'FROM_START':
-        var at1 = Blockly.Dart.getAdjusted(block, 'AT1');
+        at1 = Blockly.Dart.getAdjusted(block, 'AT1');
         break;
       case 'FROM_END':
-        var at1 = Blockly.Dart.getAdjusted(block, 'AT1', 1, false,
+        at1 = Blockly.Dart.getAdjusted(block, 'AT1', 1, false,
             Blockly.Dart.ORDER_ADDITIVE);
         at1 = list + '.length - ' + at1;
         break;
       case 'FIRST':
-        var at1 = '0';
+        at1 = '0';
         break;
       default:
         throw Error('Unhandled option (lists_getSublist).');
     }
+    let at2;
     switch (where2) {
       case 'FROM_START':
-        var at2 = Blockly.Dart.getAdjusted(block, 'AT2', 1);
+        at2 = Blockly.Dart.getAdjusted(block, 'AT2', 1);
         break;
       case 'FROM_END':
-        var at2 = Blockly.Dart.getAdjusted(block, 'AT2', 0, false,
+        at2 = Blockly.Dart.getAdjusted(block, 'AT2', 0, false,
             Blockly.Dart.ORDER_ADDITIVE);
         at2 = list + '.length - ' + at2;
         break;
@@ -351,14 +359,14 @@ Blockly.Dart['lists_getSublist'] = function(block) {
         throw Error('Unhandled option (lists_getSublist).');
     }
     if (where2 === 'LAST') {
-      var code = list + '.sublist(' + at1 + ')';
+      code = list + '.sublist(' + at1 + ')';
     } else {
-      var code = list + '.sublist(' + at1 + ', ' + at2 + ')';
+      code = list + '.sublist(' + at1 + ', ' + at2 + ')';
     }
   } else {
-    var at1 = Blockly.Dart.getAdjusted(block, 'AT1');
-    var at2 = Blockly.Dart.getAdjusted(block, 'AT2');
-    var functionName = Blockly.Dart.provideFunction_(
+    const at1 = Blockly.Dart.getAdjusted(block, 'AT1');
+    const at2 = Blockly.Dart.getAdjusted(block, 'AT2');
+    const functionName = Blockly.Dart.provideFunction_(
         'lists_get_sublist',
         ['List ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
             '(List list, String where1, num at1, String where2, num at2) {',
@@ -378,19 +386,19 @@ Blockly.Dart['lists_getSublist'] = function(block) {
          '  at2 = getAt(where2, at2) + 1;',
          '  return list.sublist(at1, at2);',
          '}']);
-    var code = functionName + '(' + list + ', \'' +
-        where1 + '\', ' + at1 + ', \'' + where2 + '\', ' + at2 + ')';
+    code = functionName + '(' + list + ', \'' + where1 + '\', ' + at1 +
+        ', \'' + where2 + '\', ' + at2 + ')';
   }
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['lists_sort'] = function(block) {
   // Block for sorting a list.
-  var list = Blockly.Dart.valueToCode(block, 'LIST',
+  const list = Blockly.Dart.valueToCode(block, 'LIST',
       Blockly.Dart.ORDER_NONE) || '[]';
-  var direction = block.getFieldValue('DIRECTION') === '1' ? 1 : -1;
-  var type = block.getFieldValue('TYPE');
-  var sortFunctionName = Blockly.Dart.provideFunction_(
+  const direction = block.getFieldValue('DIRECTION') === '1' ? 1 : -1;
+  const type = block.getFieldValue('TYPE');
+  const sortFunctionName = Blockly.Dart.provideFunction_(
       'lists_sort',
       ['List ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
           '(List list, String type, int direction) {',
@@ -414,33 +422,34 @@ Blockly.Dart['lists_sort'] = function(block) {
 
 Blockly.Dart['lists_split'] = function(block) {
   // Block for splitting text into a list, or joining a list into text.
-  var input = Blockly.Dart.valueToCode(block, 'INPUT',
+  let input = Blockly.Dart.valueToCode(block, 'INPUT',
       Blockly.Dart.ORDER_UNARY_POSTFIX);
-  var delimiter = Blockly.Dart.valueToCode(block, 'DELIM',
+  const delimiter = Blockly.Dart.valueToCode(block, 'DELIM',
       Blockly.Dart.ORDER_NONE) || '\'\'';
-  var mode = block.getFieldValue('MODE');
+  const mode = block.getFieldValue('MODE');
+  let functionName;
   if (mode === 'SPLIT') {
     if (!input) {
       input = '\'\'';
     }
-    var functionName = 'split';
+    functionName = 'split';
   } else if (mode === 'JOIN') {
     if (!input) {
       input = '[]';
     }
-    var functionName = 'join';
+    functionName = 'join';
   } else {
     throw Error('Unknown mode: ' + mode);
   }
-  var code = input + '.' + functionName + '(' + delimiter + ')';
+  const code = input + '.' + functionName + '(' + delimiter + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['lists_reverse'] = function(block) {
   // Block for reversing a list.
-  var list = Blockly.Dart.valueToCode(block, 'LIST',
+  const list = Blockly.Dart.valueToCode(block, 'LIST',
       Blockly.Dart.ORDER_NONE) || '[]';
   // XXX What should the operator precedence be for a `new`?
-  var code = 'new List.from(' + list + '.reversed)';
+  const code = 'new List.from(' + list + '.reversed)';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
diff --git a/generators/dart/logic.js b/generators/dart/logic.js
index 18f1ece2d..519937007 100644
--- a/generators/dart/logic.js
+++ b/generators/dart/logic.js
@@ -16,8 +16,8 @@ goog.require('Blockly.Dart');
 
 Blockly.Dart['controls_if'] = function(block) {
   // If/elseif/else condition.
-  var n = 0;
-  var code = '', branchCode, conditionCode;
+  let n = 0;
+  let code = '', branchCode, conditionCode;
   if (Blockly.Dart.STATEMENT_PREFIX) {
     // Automatic prefix insertion is switched off for this block.  Add manually.
     code += Blockly.Dart.injectId(Blockly.Dart.STATEMENT_PREFIX, block);
@@ -52,7 +52,7 @@ Blockly.Dart['controls_ifelse'] = Blockly.Dart['controls_if'];
 
 Blockly.Dart['logic_compare'] = function(block) {
   // Comparison operator.
-  var OPERATORS = {
+  const OPERATORS = {
     'EQ': '==',
     'NEQ': '!=',
     'LT': '<',
@@ -60,29 +60,29 @@ Blockly.Dart['logic_compare'] = function(block) {
     'GT': '>',
     'GTE': '>='
   };
-  var operator = OPERATORS[block.getFieldValue('OP')];
-  var order = (operator === '==' || operator === '!=') ?
+  const operator = OPERATORS[block.getFieldValue('OP')];
+  const order = (operator === '==' || operator === '!=') ?
       Blockly.Dart.ORDER_EQUALITY : Blockly.Dart.ORDER_RELATIONAL;
-  var argument0 = Blockly.Dart.valueToCode(block, 'A', order) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'B', order) || '0';
-  var code = argument0 + ' ' + operator + ' ' + argument1;
+  const argument0 = Blockly.Dart.valueToCode(block, 'A', order) || '0';
+  const argument1 = Blockly.Dart.valueToCode(block, 'B', order) || '0';
+  const code = argument0 + ' ' + operator + ' ' + argument1;
   return [code, order];
 };
 
 Blockly.Dart['logic_operation'] = function(block) {
   // Operations 'and', 'or'.
-  var operator = (block.getFieldValue('OP') === 'AND') ? '&&' : '||';
-  var order = (operator === '&&') ? Blockly.Dart.ORDER_LOGICAL_AND :
+  const operator = (block.getFieldValue('OP') === 'AND') ? '&&' : '||';
+  const order = (operator === '&&') ? Blockly.Dart.ORDER_LOGICAL_AND :
       Blockly.Dart.ORDER_LOGICAL_OR;
-  var argument0 = Blockly.Dart.valueToCode(block, 'A', order);
-  var argument1 = Blockly.Dart.valueToCode(block, 'B', order);
+  let argument0 = Blockly.Dart.valueToCode(block, 'A', order);
+  let argument1 = Blockly.Dart.valueToCode(block, 'B', order);
   if (!argument0 && !argument1) {
     // If there are no arguments, then the return value is false.
     argument0 = 'false';
     argument1 = 'false';
   } else {
     // Single missing arguments have no effect on the return value.
-    var defaultArgument = (operator === '&&') ? 'true' : 'false';
+    const defaultArgument = (operator === '&&') ? 'true' : 'false';
     if (!argument0) {
       argument0 = defaultArgument;
     }
@@ -90,21 +90,21 @@ Blockly.Dart['logic_operation'] = function(block) {
       argument1 = defaultArgument;
     }
   }
-  var code = argument0 + ' ' + operator + ' ' + argument1;
+  const code = argument0 + ' ' + operator + ' ' + argument1;
   return [code, order];
 };
 
 Blockly.Dart['logic_negate'] = function(block) {
   // Negation.
-  var order = Blockly.Dart.ORDER_UNARY_PREFIX;
-  var argument0 = Blockly.Dart.valueToCode(block, 'BOOL', order) || 'true';
-  var code = '!' + argument0;
+  const order = Blockly.Dart.ORDER_UNARY_PREFIX;
+  const argument0 = Blockly.Dart.valueToCode(block, 'BOOL', order) || 'true';
+  const code = '!' + argument0;
   return [code, order];
 };
 
 Blockly.Dart['logic_boolean'] = function(block) {
   // Boolean values true and false.
-  var code = (block.getFieldValue('BOOL') === 'TRUE') ? 'true' : 'false';
+  const code = (block.getFieldValue('BOOL') === 'TRUE') ? 'true' : 'false';
   return [code, Blockly.Dart.ORDER_ATOMIC];
 };
 
@@ -115,12 +115,12 @@ Blockly.Dart['logic_null'] = function(block) {
 
 Blockly.Dart['logic_ternary'] = function(block) {
   // Ternary operator.
-  var value_if = Blockly.Dart.valueToCode(block, 'IF',
+  const value_if = Blockly.Dart.valueToCode(block, 'IF',
       Blockly.Dart.ORDER_CONDITIONAL) || 'false';
-  var value_then = Blockly.Dart.valueToCode(block, 'THEN',
+  const value_then = Blockly.Dart.valueToCode(block, 'THEN',
       Blockly.Dart.ORDER_CONDITIONAL) || 'null';
-  var value_else = Blockly.Dart.valueToCode(block, 'ELSE',
+  const value_else = Blockly.Dart.valueToCode(block, 'ELSE',
       Blockly.Dart.ORDER_CONDITIONAL) || 'null';
-  var code = value_if + ' ? ' + value_then + ' : ' + value_else;
+  const code = value_if + ' ? ' + value_then + ' : ' + value_else;
   return [code, Blockly.Dart.ORDER_CONDITIONAL];
 };
diff --git a/generators/dart/loops.js b/generators/dart/loops.js
index 8cefbd4f4..6078e3d21 100644
--- a/generators/dart/loops.js
+++ b/generators/dart/loops.js
@@ -15,21 +15,22 @@ goog.require('Blockly.Dart');
 
 
 Blockly.Dart['controls_repeat_ext'] = function(block) {
+  let repeats;
   // Repeat n times.
   if (block.getField('TIMES')) {
     // Internal number.
-    var repeats = String(Number(block.getFieldValue('TIMES')));
+    repeats = String(Number(block.getFieldValue('TIMES')));
   } else {
     // External number.
-    var repeats = Blockly.Dart.valueToCode(block, 'TIMES',
+    repeats = Blockly.Dart.valueToCode(block, 'TIMES',
         Blockly.Dart.ORDER_ASSIGNMENT) || '0';
   }
-  var branch = Blockly.Dart.statementToCode(block, 'DO');
+  let branch = Blockly.Dart.statementToCode(block, 'DO');
   branch = Blockly.Dart.addLoopTrap(branch, block);
-  var code = '';
-  var loopVar = Blockly.Dart.nameDB_.getDistinctName(
+  let code = '';
+  const loopVar = Blockly.Dart.nameDB_.getDistinctName(
       'count', Blockly.VARIABLE_CATEGORY_NAME);
-  var endVar = repeats;
+  let endVar = repeats;
   if (!repeats.match(/^\w+$/) && !Blockly.isNumber(repeats)) {
     endVar = Blockly.Dart.nameDB_.getDistinctName(
         'repeat_end', Blockly.VARIABLE_CATEGORY_NAME);
@@ -46,11 +47,11 @@ Blockly.Dart['controls_repeat'] = Blockly.Dart['controls_repeat_ext'];
 
 Blockly.Dart['controls_whileUntil'] = function(block) {
   // Do while/until loop.
-  var until = block.getFieldValue('MODE') === 'UNTIL';
-  var argument0 = Blockly.Dart.valueToCode(block, 'BOOL',
+  const until = block.getFieldValue('MODE') === 'UNTIL';
+  let argument0 = Blockly.Dart.valueToCode(block, 'BOOL',
       until ? Blockly.Dart.ORDER_UNARY_PREFIX :
       Blockly.Dart.ORDER_NONE) || 'false';
-  var branch = Blockly.Dart.statementToCode(block, 'DO');
+  let branch = Blockly.Dart.statementToCode(block, 'DO');
   branch = Blockly.Dart.addLoopTrap(branch, block);
   if (until) {
     argument0 = '!' + argument0;
@@ -60,25 +61,25 @@ Blockly.Dart['controls_whileUntil'] = function(block) {
 
 Blockly.Dart['controls_for'] = function(block) {
   // For loop.
-  var variable0 = Blockly.Dart.nameDB_.getName(
+  const variable0 = Blockly.Dart.nameDB_.getName(
       block.getFieldValue('VAR'), Blockly.VARIABLE_CATEGORY_NAME);
-  var argument0 = Blockly.Dart.valueToCode(block, 'FROM',
+  const argument0 = Blockly.Dart.valueToCode(block, 'FROM',
       Blockly.Dart.ORDER_ASSIGNMENT) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'TO',
+  const argument1 = Blockly.Dart.valueToCode(block, 'TO',
       Blockly.Dart.ORDER_ASSIGNMENT) || '0';
-  var increment = Blockly.Dart.valueToCode(block, 'BY',
+  const increment = Blockly.Dart.valueToCode(block, 'BY',
       Blockly.Dart.ORDER_ASSIGNMENT) || '1';
-  var branch = Blockly.Dart.statementToCode(block, 'DO');
+  let branch = Blockly.Dart.statementToCode(block, 'DO');
   branch = Blockly.Dart.addLoopTrap(branch, block);
-  var code;
+  let code;
   if (Blockly.isNumber(argument0) && Blockly.isNumber(argument1) &&
       Blockly.isNumber(increment)) {
     // All arguments are simple numbers.
-    var up = Number(argument0) <= Number(argument1);
+    const up = Number(argument0) <= Number(argument1);
     code = 'for (' + variable0 + ' = ' + argument0 + '; ' +
         variable0 + (up ? ' <= ' : ' >= ') + argument1 + '; ' +
         variable0;
-    var step = Math.abs(Number(increment));
+    const step = Math.abs(Number(increment));
     if (step === 1) {
       code += up ? '++' : '--';
     } else {
@@ -88,13 +89,13 @@ Blockly.Dart['controls_for'] = function(block) {
   } else {
     code = '';
     // Cache non-trivial values to variables to prevent repeated look-ups.
-    var startVar = argument0;
+    let startVar = argument0;
     if (!argument0.match(/^\w+$/) && !Blockly.isNumber(argument0)) {
       startVar = Blockly.Dart.nameDB_.getDistinctName(
           variable0 + '_start', Blockly.VARIABLE_CATEGORY_NAME);
       code += 'var ' + startVar + ' = ' + argument0 + ';\n';
     }
-    var endVar = argument1;
+    let endVar = argument1;
     if (!argument1.match(/^\w+$/) && !Blockly.isNumber(argument1)) {
       endVar = Blockly.Dart.nameDB_.getDistinctName(
           variable0 + '_end', Blockly.VARIABLE_CATEGORY_NAME);
@@ -102,7 +103,7 @@ Blockly.Dart['controls_for'] = function(block) {
     }
     // Determine loop direction at start, in case one of the bounds
     // changes during loop execution.
-    var incVar = Blockly.Dart.nameDB_.getDistinctName(
+    const incVar = Blockly.Dart.nameDB_.getDistinctName(
         variable0 + '_inc', Blockly.VARIABLE_CATEGORY_NAME);
     code += 'num ' + incVar + ' = ';
     if (Blockly.isNumber(increment)) {
@@ -125,20 +126,20 @@ Blockly.Dart['controls_for'] = function(block) {
 
 Blockly.Dart['controls_forEach'] = function(block) {
   // For each loop.
-  var variable0 = Blockly.Dart.nameDB_.getName(
+  const variable0 = Blockly.Dart.nameDB_.getName(
       block.getFieldValue('VAR'), Blockly.VARIABLE_CATEGORY_NAME);
-  var argument0 = Blockly.Dart.valueToCode(block, 'LIST',
+  const argument0 = Blockly.Dart.valueToCode(block, 'LIST',
       Blockly.Dart.ORDER_ASSIGNMENT) || '[]';
-  var branch = Blockly.Dart.statementToCode(block, 'DO');
+  let branch = Blockly.Dart.statementToCode(block, 'DO');
   branch = Blockly.Dart.addLoopTrap(branch, block);
-  var code = 'for (var ' + variable0 + ' in ' + argument0 + ') {\n' +
+  const code = 'for (var ' + variable0 + ' in ' + argument0 + ') {\n' +
       branch + '}\n';
   return code;
 };
 
 Blockly.Dart['controls_flow_statements'] = function(block) {
   // Flow statements: continue, break.
-  var xfix = '';
+  let xfix = '';
   if (Blockly.Dart.STATEMENT_PREFIX) {
     // Automatic prefix insertion is switched off for this block.  Add manually.
     xfix += Blockly.Dart.injectId(Blockly.Dart.STATEMENT_PREFIX, block);
@@ -149,7 +150,7 @@ Blockly.Dart['controls_flow_statements'] = function(block) {
     xfix += Blockly.Dart.injectId(Blockly.Dart.STATEMENT_SUFFIX, block);
   }
   if (Blockly.Dart.STATEMENT_PREFIX) {
-    var loop = Blockly.Constants.Loops
+    const loop = Blockly.Constants.Loops
         .CONTROL_FLOW_IN_LOOP_CHECK_MIXIN.getSurroundLoop(block);
     if (loop && !loop.suppressPrefixSuffix) {
       // Inject loop's statement prefix here since the regular one at the end
diff --git a/generators/dart/math.js b/generators/dart/math.js
index c57181b74..4a70ec437 100644
--- a/generators/dart/math.js
+++ b/generators/dart/math.js
@@ -18,8 +18,8 @@ Blockly.Dart.addReservedWords('Math');
 
 Blockly.Dart['math_number'] = function(block) {
   // Numeric value.
-  var code = Number(block.getFieldValue('NUM'));
-  var order;
+  let code = Number(block.getFieldValue('NUM'));
+  let order;
   if (code === Infinity) {
     code = 'double.infinity';
     order = Blockly.Dart.ORDER_UNARY_POSTFIX;
@@ -37,19 +37,19 @@ Blockly.Dart['math_number'] = function(block) {
 
 Blockly.Dart['math_arithmetic'] = function(block) {
   // Basic arithmetic operators, and power.
-  var OPERATORS = {
+  const OPERATORS = {
     'ADD': [' + ', Blockly.Dart.ORDER_ADDITIVE],
     'MINUS': [' - ', Blockly.Dart.ORDER_ADDITIVE],
     'MULTIPLY': [' * ', Blockly.Dart.ORDER_MULTIPLICATIVE],
     'DIVIDE': [' / ', Blockly.Dart.ORDER_MULTIPLICATIVE],
     'POWER': [null, Blockly.Dart.ORDER_NONE]  // Handle power separately.
   };
-  var tuple = OPERATORS[block.getFieldValue('OP')];
-  var operator = tuple[0];
-  var order = tuple[1];
-  var argument0 = Blockly.Dart.valueToCode(block, 'A', order) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'B', order) || '0';
-  var code;
+  const tuple = OPERATORS[block.getFieldValue('OP')];
+  const operator = tuple[0];
+  const order = tuple[1];
+  const argument0 = Blockly.Dart.valueToCode(block, 'A', order) || '0';
+  const argument1 = Blockly.Dart.valueToCode(block, 'B', order) || '0';
+  let code;
   // Power in Dart requires a special case since it has no operator.
   if (!operator) {
     Blockly.Dart.definitions_['import_dart_math'] =
@@ -63,9 +63,9 @@ Blockly.Dart['math_arithmetic'] = function(block) {
 
 Blockly.Dart['math_single'] = function(block) {
   // Math operators with single operand.
-  var operator = block.getFieldValue('OP');
-  var code;
-  var arg;
+  const operator = block.getFieldValue('OP');
+  let code;
+  let arg;
   if (operator === 'NEG') {
     // Negation is a special case given its different operator precedence.
     arg = Blockly.Dart.valueToCode(block, 'NUM',
@@ -152,7 +152,7 @@ Blockly.Dart['math_single'] = function(block) {
 
 Blockly.Dart['math_constant'] = function(block) {
   // Constants: PI, E, the Golden Ratio, sqrt(2), 1/sqrt(2), INFINITY.
-  var CONSTANTS = {
+  const CONSTANTS = {
     'PI': ['Math.pi', Blockly.Dart.ORDER_UNARY_POSTFIX],
     'E': ['Math.e', Blockly.Dart.ORDER_UNARY_POSTFIX],
     'GOLDEN_RATIO':
@@ -161,7 +161,7 @@ Blockly.Dart['math_constant'] = function(block) {
     'SQRT1_2': ['Math.sqrt1_2', Blockly.Dart.ORDER_UNARY_POSTFIX],
     'INFINITY': ['double.infinity', Blockly.Dart.ORDER_ATOMIC]
   };
-  var constant = block.getFieldValue('CONSTANT');
+  const constant = block.getFieldValue('CONSTANT');
   if (constant !== 'INFINITY') {
     Blockly.Dart.definitions_['import_dart_math'] =
         'import \'dart:math\' as Math;';
@@ -172,18 +172,18 @@ Blockly.Dart['math_constant'] = function(block) {
 Blockly.Dart['math_number_property'] = function(block) {
   // Check if a number is even, odd, prime, whole, positive, or negative
   // or if it is divisible by certain number. Returns true or false.
-  var number_to_check = Blockly.Dart.valueToCode(block, 'NUMBER_TO_CHECK',
+  const number_to_check = Blockly.Dart.valueToCode(block, 'NUMBER_TO_CHECK',
       Blockly.Dart.ORDER_MULTIPLICATIVE);
   if (!number_to_check) {
     return ['false', Blockly.Dart.ORDER_ATOMIC];
   }
-  var dropdown_property = block.getFieldValue('PROPERTY');
-  var code;
+  const dropdown_property = block.getFieldValue('PROPERTY');
+  let code;
   if (dropdown_property === 'PRIME') {
     // Prime is a special case as it is not a one-liner test.
     Blockly.Dart.definitions_['import_dart_math'] =
         'import \'dart:math\' as Math;';
-    var functionName = Blockly.Dart.provideFunction_(
+    const functionName = Blockly.Dart.provideFunction_(
         'math_isPrime',
         ['bool ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ + '(n) {',
          '  // https://en.wikipedia.org/wiki/Primality_test#Naive_methods',
@@ -224,7 +224,7 @@ Blockly.Dart['math_number_property'] = function(block) {
       code = number_to_check + ' < 0';
       break;
     case 'DIVISIBLE_BY':
-      var divisor = Blockly.Dart.valueToCode(block, 'DIVISOR',
+      const divisor = Blockly.Dart.valueToCode(block, 'DIVISOR',
           Blockly.Dart.ORDER_MULTIPLICATIVE);
       if (!divisor) {
         return ['false', Blockly.Dart.ORDER_ATOMIC];
@@ -237,9 +237,9 @@ Blockly.Dart['math_number_property'] = function(block) {
 
 Blockly.Dart['math_change'] = function(block) {
   // Add to a variable in place.
-  var argument0 = Blockly.Dart.valueToCode(block, 'DELTA',
+  const argument0 = Blockly.Dart.valueToCode(block, 'DELTA',
       Blockly.Dart.ORDER_ADDITIVE) || '0';
-  var varName = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
+  const varName = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
       Blockly.VARIABLE_CATEGORY_NAME);
   return varName + ' = (' + varName + ' is num ? ' + varName + ' : 0) + ' +
       argument0 + ';\n';
@@ -252,13 +252,13 @@ Blockly.Dart['math_trig'] = Blockly.Dart['math_single'];
 
 Blockly.Dart['math_on_list'] = function(block) {
   // Math functions for lists.
-  var func = block.getFieldValue('OP');
-  var list = Blockly.Dart.valueToCode(block, 'LIST',
+  const func = block.getFieldValue('OP');
+  const list = Blockly.Dart.valueToCode(block, 'LIST',
       Blockly.Dart.ORDER_NONE) || '[]';
-  var code;
+  let code;
   switch (func) {
-    case 'SUM':
-      var functionName = Blockly.Dart.provideFunction_(
+    case 'SUM': {
+      const functionName = Blockly.Dart.provideFunction_(
           'math_sum',
           ['num ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List<num> myList) {',
@@ -268,10 +268,11 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'MIN':
+    }
+    case 'MIN': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'math_min',
           ['num ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List<num> myList) {',
@@ -283,10 +284,11 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'MAX':
+    }
+    case 'MAX': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'math_max',
           ['num ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List<num> myList) {',
@@ -298,10 +300,11 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'AVERAGE':
+    }
+    case 'AVERAGE': {
       // This operation exclude null and values that are not int or float:
       //   math_mean([null,null,"aString",1,9]) -> 5.0
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'math_mean',
           ['num ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List myList) {',
@@ -315,8 +318,9 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'MEDIAN':
-      var functionName = Blockly.Dart.provideFunction_(
+    }
+    case 'MEDIAN': {
+      const functionName = Blockly.Dart.provideFunction_(
           'math_median',
           ['num ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List myList) {',
@@ -337,13 +341,14 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'MODE':
+    }
+    case 'MODE': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
       // As a list of numbers can contain more than one mode,
       // the returned result is provided as an array.
       // Mode of [3, 'x', 'x', 1, 1, 2, '3'] -> ['x', 1]
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'math_modes',
           ['List ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List values) {',
@@ -376,10 +381,11 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'STD_DEV':
+    }
+    case 'STD_DEV': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'math_standard_deviation',
           ['num ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List myList) {',
@@ -398,10 +404,11 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
-    case 'RANDOM':
+    }
+    case 'RANDOM': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'math_random_item',
           ['dynamic ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(List myList) {',
@@ -410,6 +417,7 @@ Blockly.Dart['math_on_list'] = function(block) {
            '}']);
       code = functionName + '(' + list + ')';
       break;
+    }
     default:
       throw Error('Unknown operator: ' + func);
   }
@@ -418,11 +426,11 @@ Blockly.Dart['math_on_list'] = function(block) {
 
 Blockly.Dart['math_modulo'] = function(block) {
   // Remainder computation.
-  var argument0 = Blockly.Dart.valueToCode(block, 'DIVIDEND',
+  const argument0 = Blockly.Dart.valueToCode(block, 'DIVIDEND',
       Blockly.Dart.ORDER_MULTIPLICATIVE) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'DIVISOR',
+  const argument1 = Blockly.Dart.valueToCode(block, 'DIVISOR',
       Blockly.Dart.ORDER_MULTIPLICATIVE) || '0';
-  var code = argument0 + ' % ' + argument1;
+  const code = argument0 + ' % ' + argument1;
   return [code, Blockly.Dart.ORDER_MULTIPLICATIVE];
 };
 
@@ -430,13 +438,13 @@ Blockly.Dart['math_constrain'] = function(block) {
   // Constrain a number between two limits.
   Blockly.Dart.definitions_['import_dart_math'] =
       'import \'dart:math\' as Math;';
-  var argument0 = Blockly.Dart.valueToCode(block, 'VALUE',
+  const argument0 = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_NONE) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'LOW',
+  const argument1 = Blockly.Dart.valueToCode(block, 'LOW',
       Blockly.Dart.ORDER_NONE) || '0';
-  var argument2 = Blockly.Dart.valueToCode(block, 'HIGH',
+  const argument2 = Blockly.Dart.valueToCode(block, 'HIGH',
       Blockly.Dart.ORDER_NONE) || 'double.infinity';
-  var code = 'Math.min(Math.max(' + argument0 + ', ' + argument1 + '), ' +
+  const code = 'Math.min(Math.max(' + argument0 + ', ' + argument1 + '), ' +
       argument2 + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
@@ -445,11 +453,11 @@ Blockly.Dart['math_random_int'] = function(block) {
   // Random integer between [X] and [Y].
   Blockly.Dart.definitions_['import_dart_math'] =
       'import \'dart:math\' as Math;';
-  var argument0 = Blockly.Dart.valueToCode(block, 'FROM',
+  const argument0 = Blockly.Dart.valueToCode(block, 'FROM',
       Blockly.Dart.ORDER_NONE) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'TO',
+  const argument1 = Blockly.Dart.valueToCode(block, 'TO',
       Blockly.Dart.ORDER_NONE) || '0';
-  var functionName = Blockly.Dart.provideFunction_(
+  const functionName = Blockly.Dart.provideFunction_(
       'math_random_int',
       ['int ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ + '(num a, num b) {',
        '  if (a > b) {',
@@ -460,7 +468,7 @@ Blockly.Dart['math_random_int'] = function(block) {
        '  }',
        '  return new Math.Random().nextInt(b - a + 1) + a;',
        '}']);
-  var code = functionName + '(' + argument0 + ', ' + argument1 + ')';
+  const code = functionName + '(' + argument0 + ', ' + argument1 + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
@@ -475,9 +483,9 @@ Blockly.Dart['math_atan2'] = function(block) {
   // Arctangent of point (X, Y) in degrees from -180 to 180.
   Blockly.Dart.definitions_['import_dart_math'] =
       'import \'dart:math\' as Math;';
-  var argument0 = Blockly.Dart.valueToCode(block, 'X',
+  const argument0 = Blockly.Dart.valueToCode(block, 'X',
       Blockly.Dart.ORDER_NONE) || '0';
-  var argument1 = Blockly.Dart.valueToCode(block, 'Y',
+  const argument1 = Blockly.Dart.valueToCode(block, 'Y',
       Blockly.Dart.ORDER_NONE) || '0';
   return ['Math.atan2(' + argument1 + ', ' + argument0 + ') / Math.pi * 180',
       Blockly.Dart.ORDER_MULTIPLICATIVE];
diff --git a/generators/dart/procedures.js b/generators/dart/procedures.js
index 3aa6ce215..bb539b8d1 100644
--- a/generators/dart/procedures.js
+++ b/generators/dart/procedures.js
@@ -16,9 +16,9 @@ goog.require('Blockly.Dart');
 
 Blockly.Dart['procedures_defreturn'] = function(block) {
   // Define a procedure with a return value.
-  var funcName = Blockly.Dart.nameDB_.getName(block.getFieldValue('NAME'),
+  const funcName = Blockly.Dart.nameDB_.getName(block.getFieldValue('NAME'),
       Blockly.PROCEDURE_CATEGORY_NAME);
-  var xfix1 = '';
+  let xfix1 = '';
   if (Blockly.Dart.STATEMENT_PREFIX) {
     xfix1 += Blockly.Dart.injectId(Blockly.Dart.STATEMENT_PREFIX, block);
   }
@@ -28,16 +28,16 @@ Blockly.Dart['procedures_defreturn'] = function(block) {
   if (xfix1) {
     xfix1 = Blockly.Dart.prefixLines(xfix1, Blockly.Dart.INDENT);
   }
-  var loopTrap = '';
+  let loopTrap = '';
   if (Blockly.Dart.INFINITE_LOOP_TRAP) {
     loopTrap = Blockly.Dart.prefixLines(
         Blockly.Dart.injectId(Blockly.Dart.INFINITE_LOOP_TRAP, block),
         Blockly.Dart.INDENT);
   }
-  var branch = Blockly.Dart.statementToCode(block, 'STACK');
-  var returnValue = Blockly.Dart.valueToCode(block, 'RETURN',
+  const branch = Blockly.Dart.statementToCode(block, 'STACK');
+  let returnValue = Blockly.Dart.valueToCode(block, 'RETURN',
       Blockly.Dart.ORDER_NONE) || '';
-  var xfix2 = '';
+  let xfix2 = '';
   if (branch && returnValue) {
     // After executing the function body, revisit this block for the return.
     xfix2 = xfix1;
@@ -45,14 +45,14 @@ Blockly.Dart['procedures_defreturn'] = function(block) {
   if (returnValue) {
     returnValue = Blockly.Dart.INDENT + 'return ' + returnValue + ';\n';
   }
-  var returnType = returnValue ? 'dynamic' : 'void';
-  var args = [];
-  var variables = block.getVars();
-  for (var i = 0; i < variables.length; i++) {
+  const returnType = returnValue ? 'dynamic' : 'void';
+  const args = [];
+  const variables = block.getVars();
+  for (let i = 0; i < variables.length; i++) {
     args[i] = Blockly.Dart.nameDB_.getName(variables[i],
         Blockly.VARIABLE_CATEGORY_NAME);
   }
-  var code = returnType + ' ' + funcName + '(' + args.join(', ') + ') {\n' +
+  let code = returnType + ' ' + funcName + '(' + args.join(', ') + ') {\n' +
       xfix1 + loopTrap + branch + xfix2 + returnValue + '}';
   code = Blockly.Dart.scrub_(block, code);
   // Add % so as not to collide with helper functions in definitions list.
@@ -66,15 +66,15 @@ Blockly.Dart['procedures_defnoreturn'] = Blockly.Dart['procedures_defreturn'];
 
 Blockly.Dart['procedures_callreturn'] = function(block) {
   // Call a procedure with a return value.
-  var funcName = Blockly.Dart.nameDB_.getName(block.getFieldValue('NAME'),
+  const funcName = Blockly.Dart.nameDB_.getName(block.getFieldValue('NAME'),
       Blockly.PROCEDURE_CATEGORY_NAME);
-  var args = [];
-  var variables = block.getVars();
-  for (var i = 0; i < variables.length; i++) {
+  const args = [];
+  const variables = block.getVars();
+  for (let i = 0; i < variables.length; i++) {
     args[i] = Blockly.Dart.valueToCode(block, 'ARG' + i,
         Blockly.Dart.ORDER_NONE) || 'null';
   }
-  var code = funcName + '(' + args.join(', ') + ')';
+  let code = funcName + '(' + args.join(', ') + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
@@ -82,15 +82,15 @@ Blockly.Dart['procedures_callnoreturn'] = function(block) {
   // Call a procedure with no return value.
   // Generated code is for a function call as a statement is the same as a
   // function call as a value, with the addition of line ending.
-  var tuple = Blockly.Dart['procedures_callreturn'](block);
+  const tuple = Blockly.Dart['procedures_callreturn'](block);
   return tuple[0] + ';\n';
 };
 
 Blockly.Dart['procedures_ifreturn'] = function(block) {
   // Conditionally return value from a procedure.
-  var condition = Blockly.Dart.valueToCode(block, 'CONDITION',
+  const condition = Blockly.Dart.valueToCode(block, 'CONDITION',
       Blockly.Dart.ORDER_NONE) || 'false';
-  var code = 'if (' + condition + ') {\n';
+  let code = 'if (' + condition + ') {\n';
   if (Blockly.Dart.STATEMENT_SUFFIX) {
     // Inject any statement suffix here since the regular one at the end
     // will not get executed if the return is triggered.
@@ -99,7 +99,7 @@ Blockly.Dart['procedures_ifreturn'] = function(block) {
         Blockly.Dart.INDENT);
   }
   if (block.hasReturnValue_) {
-    var value = Blockly.Dart.valueToCode(block, 'VALUE',
+    const value = Blockly.Dart.valueToCode(block, 'VALUE',
         Blockly.Dart.ORDER_NONE) || 'null';
     code += Blockly.Dart.INDENT + 'return ' + value + ';\n';
   } else {
diff --git a/generators/dart/text.js b/generators/dart/text.js
index cc9963dfc..c589571e2 100644
--- a/generators/dart/text.js
+++ b/generators/dart/text.js
@@ -18,14 +18,14 @@ Blockly.Dart.addReservedWords('Html,Math');
 
 Blockly.Dart['text'] = function(block) {
   // Text value.
-  var code = Blockly.Dart.quote_(block.getFieldValue('TEXT'));
+  const code = Blockly.Dart.quote_(block.getFieldValue('TEXT'));
   return [code, Blockly.Dart.ORDER_ATOMIC];
 };
 
 Blockly.Dart['text_multiline'] = function(block) {
   // Text value.
-  var code = Blockly.Dart.multiline_quote_(block.getFieldValue('TEXT'));
-  var order = code.indexOf('+') !== -1 ? Blockly.Dart.ORDER_ADDITIVE :
+  const code = Blockly.Dart.multiline_quote_(block.getFieldValue('TEXT'));
+  const order = code.indexOf('+') !== -1 ? Blockly.Dart.ORDER_ADDITIVE :
       Blockly.Dart.ORDER_ATOMIC;
   return [code, order];
 };
@@ -35,54 +35,56 @@ Blockly.Dart['text_join'] = function(block) {
   switch (block.itemCount_) {
     case 0:
       return ['\'\'', Blockly.Dart.ORDER_ATOMIC];
-    case 1:
-      var element = Blockly.Dart.valueToCode(block, 'ADD0',
+    case 1: {
+      const element = Blockly.Dart.valueToCode(block, 'ADD0',
               Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
-      var code = element + '.toString()';
+      const code = element + '.toString()';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
-    default:
-      var elements = new Array(block.itemCount_);
-      for (var i = 0; i < block.itemCount_; i++) {
+    }
+    default: {
+      const elements = new Array(block.itemCount_);
+      for (let i = 0; i < block.itemCount_; i++) {
         elements[i] = Blockly.Dart.valueToCode(block, 'ADD' + i,
                 Blockly.Dart.ORDER_NONE) || '\'\'';
       }
-      var code = '[' + elements.join(',') + '].join()';
+      const code = '[' + elements.join(',') + '].join()';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
+    }
   }
 };
 
 Blockly.Dart['text_append'] = function(block) {
   // Append to a variable in place.
-  var varName = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
+  const varName = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
       Blockly.VARIABLE_CATEGORY_NAME);
-  var value = Blockly.Dart.valueToCode(block, 'TEXT',
+  const value = Blockly.Dart.valueToCode(block, 'TEXT',
       Blockly.Dart.ORDER_NONE) || '\'\'';
   return varName + ' = [' + varName + ', ' + value + '].join();\n';
 };
 
 Blockly.Dart['text_length'] = function(block) {
   // String or array length.
-  var text = Blockly.Dart.valueToCode(block, 'VALUE',
+  const text = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
   return [text + '.length', Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['text_isEmpty'] = function(block) {
   // Is the string null or array empty?
-  var text = Blockly.Dart.valueToCode(block, 'VALUE',
+  const text = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
   return [text + '.isEmpty', Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['text_indexOf'] = function(block) {
   // Search the text for a substring.
-  var operator = block.getFieldValue('END') === 'FIRST' ?
+  const operator = block.getFieldValue('END') === 'FIRST' ?
       'indexOf' : 'lastIndexOf';
-  var substring = Blockly.Dart.valueToCode(block, 'FIND',
+  const substring = Blockly.Dart.valueToCode(block, 'FIND',
       Blockly.Dart.ORDER_NONE) || '\'\'';
-  var text = Blockly.Dart.valueToCode(block, 'VALUE',
+  const text = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
-  var code = text + '.' + operator + '(' + substring + ')';
+  const code = text + '.' + operator + '(' + substring + ')';
   if (block.workspace.options.oneBasedIndex) {
     return [code + ' + 1', Blockly.Dart.ORDER_ADDITIVE];
   }
@@ -92,82 +94,90 @@ Blockly.Dart['text_indexOf'] = function(block) {
 Blockly.Dart['text_charAt'] = function(block) {
   // Get letter at index.
   // Note: Until January 2013 this block did not have the WHERE input.
-  var where = block.getFieldValue('WHERE') || 'FROM_START';
-  var textOrder = (where === 'FIRST' || where === 'FROM_START') ?
+  const where = block.getFieldValue('WHERE') || 'FROM_START';
+  const textOrder = (where === 'FIRST' || where === 'FROM_START') ?
       Blockly.Dart.ORDER_UNARY_POSTFIX : Blockly.Dart.ORDER_NONE;
-  var text = Blockly.Dart.valueToCode(block, 'VALUE', textOrder) || '\'\'';
+  const text = Blockly.Dart.valueToCode(block, 'VALUE', textOrder) || '\'\'';
+  let at;
   switch (where) {
-    case 'FIRST':
-      var code = text + '[0]';
+    case 'FIRST': {
+      const code = text + '[0]';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
-    case 'FROM_START':
-      var at = Blockly.Dart.getAdjusted(block, 'AT');
-      var code = text + '[' + at + ']';
+    }
+    case 'FROM_START': {
+      at = Blockly.Dart.getAdjusted(block, 'AT');
+      const code = text + '[' + at + ']';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
+    }
     case 'LAST':
       at = 1;
       // Fall through.
-    case 'FROM_END':
-      var at = Blockly.Dart.getAdjusted(block, 'AT', 1);
-      var functionName = Blockly.Dart.provideFunction_(
+    case 'FROM_END': {
+      at = Blockly.Dart.getAdjusted(block, 'AT', 1);
+      const functionName = Blockly.Dart.provideFunction_(
           'text_get_from_end',
           ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(String text, num x) {',
            '  return text[text.length - x];',
            '}']);
-      code = functionName + '(' + text + ', ' + at + ')';
+      const code = functionName + '(' + text + ', ' + at + ')';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
-    case 'RANDOM':
+    }
+    case 'RANDOM': {
       Blockly.Dart.definitions_['import_dart_math'] =
           'import \'dart:math\' as Math;';
-      var functionName = Blockly.Dart.provideFunction_(
+      const functionName = Blockly.Dart.provideFunction_(
           'text_random_letter',
           ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
               '(String text) {',
            '  int x = new Math.Random().nextInt(text.length);',
            '  return text[x];',
            '}']);
-      code = functionName + '(' + text + ')';
+      const code = functionName + '(' + text + ')';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
+    }
   }
   throw Error('Unhandled option (text_charAt).');
 };
 
 Blockly.Dart['text_getSubstring'] = function(block) {
   // Get substring.
-  var where1 = block.getFieldValue('WHERE1');
-  var where2 = block.getFieldValue('WHERE2');
-  var requiresLengthCall = (where1 !== 'FROM_END' && where2 === 'FROM_START');
-  var textOrder = requiresLengthCall ? Blockly.Dart.ORDER_UNARY_POSTFIX :
+  const where1 = block.getFieldValue('WHERE1');
+  const where2 = block.getFieldValue('WHERE2');
+  const requiresLengthCall = (where1 !== 'FROM_END' && where2 === 'FROM_START');
+  const textOrder = requiresLengthCall ? Blockly.Dart.ORDER_UNARY_POSTFIX :
       Blockly.Dart.ORDER_NONE;
-  var text = Blockly.Dart.valueToCode(block, 'STRING', textOrder) || '\'\'';
+  const text = Blockly.Dart.valueToCode(block, 'STRING', textOrder) || '\'\'';
+  let code;
   if (where1 === 'FIRST' && where2 === 'LAST') {
-    var code = text;
+    code = text;
     return [code, Blockly.Dart.ORDER_NONE];
   } else if (text.match(/^'?\w+'?$/) || requiresLengthCall) {
     // If the text is a variable or literal or doesn't require a call for
     // length, don't generate a helper function.
+    let at1;
     switch (where1) {
       case 'FROM_START':
-        var at1 = Blockly.Dart.getAdjusted(block, 'AT1');
+        at1 = Blockly.Dart.getAdjusted(block, 'AT1');
         break;
       case 'FROM_END':
-        var at1 = Blockly.Dart.getAdjusted(block, 'AT1', 1, false,
+        at1 = Blockly.Dart.getAdjusted(block, 'AT1', 1, false,
             Blockly.Dart.ORDER_ADDITIVE);
         at1 = text + '.length - ' + at1;
         break;
       case 'FIRST':
-        var at1 = '0';
+        at1 = '0';
         break;
       default:
         throw Error('Unhandled option (text_getSubstring).');
     }
+    let at2;
     switch (where2) {
       case 'FROM_START':
-        var at2 = Blockly.Dart.getAdjusted(block, 'AT2', 1);
+        at2 = Blockly.Dart.getAdjusted(block, 'AT2', 1);
         break;
       case 'FROM_END':
-        var at2 = Blockly.Dart.getAdjusted(block, 'AT2', 0, false,
+        at2 = Blockly.Dart.getAdjusted(block, 'AT2', 0, false,
             Blockly.Dart.ORDER_ADDITIVE);
         at2 = text + '.length - ' + at2;
         break;
@@ -176,15 +186,16 @@ Blockly.Dart['text_getSubstring'] = function(block) {
       default:
         throw Error('Unhandled option (text_getSubstring).');
     }
+
     if (where2 === 'LAST') {
-      var code = text + '.substring(' + at1 + ')';
+      code = text + '.substring(' + at1 + ')';
     } else {
-      var code = text + '.substring(' + at1 + ', ' + at2 + ')';
+      code = text + '.substring(' + at1 + ', ' + at2 + ')';
     }
   } else {
-    var at1 = Blockly.Dart.getAdjusted(block, 'AT1');
-    var at2 = Blockly.Dart.getAdjusted(block, 'AT2');
-    var functionName = Blockly.Dart.provideFunction_(
+    const at1 = Blockly.Dart.getAdjusted(block, 'AT1');
+    const at2 = Blockly.Dart.getAdjusted(block, 'AT2');
+    const functionName = Blockly.Dart.provideFunction_(
         'text_get_substring',
         ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
             '(String text, String where1, num at1, String where2, num at2) {',
@@ -204,7 +215,7 @@ Blockly.Dart['text_getSubstring'] = function(block) {
          '  at2 = getAt(where2, at2) + 1;',
          '  return text.substring(at1, at2);',
          '}']);
-    var code = functionName + '(' + text + ', \'' +
+    code = functionName + '(' + text + ', \'' +
         where1 + '\', ' + at1 + ', \'' + where2 + '\', ' + at2 + ')';
   }
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
@@ -212,21 +223,22 @@ Blockly.Dart['text_getSubstring'] = function(block) {
 
 Blockly.Dart['text_changeCase'] = function(block) {
   // Change capitalization.
-  var OPERATORS = {
+  const OPERATORS = {
     'UPPERCASE': '.toUpperCase()',
     'LOWERCASE': '.toLowerCase()',
     'TITLECASE': null
   };
-  var operator = OPERATORS[block.getFieldValue('CASE')];
-  var textOrder = operator ? Blockly.Dart.ORDER_UNARY_POSTFIX :
+  const operator = OPERATORS[block.getFieldValue('CASE')];
+  const textOrder = operator ? Blockly.Dart.ORDER_UNARY_POSTFIX :
       Blockly.Dart.ORDER_NONE;
-  var text = Blockly.Dart.valueToCode(block, 'TEXT', textOrder) || '\'\'';
+  const text = Blockly.Dart.valueToCode(block, 'TEXT', textOrder) || '\'\'';
+  let code;
   if (operator) {
     // Upper and lower case are functions built into Dart.
-    var code = text + operator;
+    code = text + operator;
   } else {
     // Title case is not a native Dart function.  Define one.
-    var functionName = Blockly.Dart.provideFunction_(
+    const functionName = Blockly.Dart.provideFunction_(
         'text_toTitleCase',
         ['String ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
             '(String str) {',
@@ -243,27 +255,27 @@ Blockly.Dart['text_changeCase'] = function(block) {
          '  }',
          '  return title.toString();',
          '}']);
-    var code = functionName + '(' + text + ')';
+    code = functionName + '(' + text + ')';
   }
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['text_trim'] = function(block) {
   // Trim spaces.
-  var OPERATORS = {
+  const OPERATORS = {
     'LEFT': '.replaceFirst(new RegExp(r\'^\\s+\'), \'\')',
     'RIGHT': '.replaceFirst(new RegExp(r\'\\s+$\'), \'\')',
     'BOTH': '.trim()'
   };
-  var operator = OPERATORS[block.getFieldValue('MODE')];
-  var text = Blockly.Dart.valueToCode(block, 'TEXT',
+  const operator = OPERATORS[block.getFieldValue('MODE')];
+  const text = Blockly.Dart.valueToCode(block, 'TEXT',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
   return [text + operator, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['text_print'] = function(block) {
   // Print statement.
-  var msg = Blockly.Dart.valueToCode(block, 'TEXT',
+  const msg = Blockly.Dart.valueToCode(block, 'TEXT',
       Blockly.Dart.ORDER_NONE) || '\'\'';
   return 'print(' + msg + ');\n';
 };
@@ -272,16 +284,17 @@ Blockly.Dart['text_prompt_ext'] = function(block) {
   // Prompt function.
   Blockly.Dart.definitions_['import_dart_html'] =
       'import \'dart:html\' as Html;';
+  let msg;
   if (block.getField('TEXT')) {
     // Internal message.
-    var msg = Blockly.Dart.quote_(block.getFieldValue('TEXT'));
+    msg = Blockly.Dart.quote_(block.getFieldValue('TEXT'));
   } else {
     // External message.
-    var msg = Blockly.Dart.valueToCode(block, 'TEXT',
+    msg = Blockly.Dart.valueToCode(block, 'TEXT',
         Blockly.Dart.ORDER_NONE) || '\'\'';
   }
-  var code = 'Html.window.prompt(' + msg + ', \'\')';
-  var toNumber = block.getFieldValue('TYPE') === 'NUMBER';
+  let code = 'Html.window.prompt(' + msg + ', \'\')';
+  const toNumber = block.getFieldValue('TYPE') === 'NUMBER';
   if (toNumber) {
     Blockly.Dart.definitions_['import_dart_math'] =
         'import \'dart:math\' as Math;';
@@ -293,12 +306,12 @@ Blockly.Dart['text_prompt_ext'] = function(block) {
 Blockly.Dart['text_prompt'] = Blockly.Dart['text_prompt_ext'];
 
 Blockly.Dart['text_count'] = function(block) {
-  var text = Blockly.Dart.valueToCode(block, 'TEXT',
+  const text = Blockly.Dart.valueToCode(block, 'TEXT',
       Blockly.Dart.ORDER_NONE) || '\'\'';
-  var sub = Blockly.Dart.valueToCode(block, 'SUB',
+  const sub = Blockly.Dart.valueToCode(block, 'SUB',
       Blockly.Dart.ORDER_NONE) || '\'\'';
   // Substring count is not a native Dart function.  Define one.
-  var functionName = Blockly.Dart.provideFunction_(
+  const functionName = Blockly.Dart.provideFunction_(
       'text_count',
       ['int ' + Blockly.Dart.FUNCTION_NAME_PLACEHOLDER_ +
         '(String haystack, String needle) {',
@@ -316,18 +329,18 @@ Blockly.Dart['text_count'] = function(block) {
         '  }',
         '  return count;',
         '}']);
-  var code = functionName + '(' + text + ', ' + sub + ')';
+  const code = functionName + '(' + text + ', ' + sub + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
 Blockly.Dart['text_replace'] = function(block) {
-  var text = Blockly.Dart.valueToCode(block, 'TEXT',
+  const text = Blockly.Dart.valueToCode(block, 'TEXT',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
-  var from = Blockly.Dart.valueToCode(block, 'FROM',
+  const from = Blockly.Dart.valueToCode(block, 'FROM',
       Blockly.Dart.ORDER_NONE) || '\'\'';
-  var to = Blockly.Dart.valueToCode(block, 'TO',
+  const to = Blockly.Dart.valueToCode(block, 'TO',
       Blockly.Dart.ORDER_NONE) || '\'\'';
-  var code = text + '.replaceAll(' + from + ', ' + to + ')';
+  const code = text + '.replaceAll(' + from + ', ' + to + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
 
@@ -335,8 +348,8 @@ Blockly.Dart['text_reverse'] = function(block) {
   // There isn't a sensible way to do this in Dart. See:
   // http://stackoverflow.com/a/21613700/3529104
   // Implementing something is possibly better than not implementing anything?
-  var text = Blockly.Dart.valueToCode(block, 'TEXT',
+  const text = Blockly.Dart.valueToCode(block, 'TEXT',
       Blockly.Dart.ORDER_UNARY_POSTFIX) || '\'\'';
-  var code = 'new String.fromCharCodes(' + text + '.runes.toList().reversed)';
+  const code = 'new String.fromCharCodes(' + text + '.runes.toList().reversed)';
   return [code, Blockly.Dart.ORDER_UNARY_PREFIX];
 };
diff --git a/generators/dart/variables.js b/generators/dart/variables.js
index 9eb56e1de..31506d3b3 100644
--- a/generators/dart/variables.js
+++ b/generators/dart/variables.js
@@ -16,16 +16,16 @@ goog.require('Blockly.Dart');
 
 Blockly.Dart['variables_get'] = function(block) {
   // Variable getter.
-  var code = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
+  const code = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
       Blockly.VARIABLE_CATEGORY_NAME);
   return [code, Blockly.Dart.ORDER_ATOMIC];
 };
 
 Blockly.Dart['variables_set'] = function(block) {
   // Variable setter.
-  var argument0 = Blockly.Dart.valueToCode(block, 'VALUE',
+  const argument0 = Blockly.Dart.valueToCode(block, 'VALUE',
       Blockly.Dart.ORDER_ASSIGNMENT) || '0';
-  var varName = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
+  const varName = Blockly.Dart.nameDB_.getName(block.getFieldValue('VAR'),
       Blockly.VARIABLE_CATEGORY_NAME);
   return varName + ' = ' + argument0 + ';\n';
 };
diff --git a/tests/deps.mocha.js b/tests/deps.mocha.js
index c223377a6..2524297e7 100644
--- a/tests/deps.mocha.js
+++ b/tests/deps.mocha.js
@@ -262,14 +262,14 @@ goog.addDependency('../../core/workspace_svg.js', ['Blockly.WorkspaceSvg'], ['Bl
 goog.addDependency('../../core/xml.js', ['Blockly.Xml'], ['Blockly.Events.utils', 'Blockly.inputTypes', 'Blockly.utils.Size', 'Blockly.utils.dom', 'Blockly.utils.xml'], {'lang': 'es6', 'module': 'goog'});
 goog.addDependency('../../core/zoom_controls.js', ['Blockly.ZoomControls'], ['Blockly.ComponentManager', 'Blockly.Css', 'Blockly.Events.Click', 'Blockly.Events.utils', 'Blockly.IPositionable', 'Blockly.Touch', 'Blockly.browserEvents', 'Blockly.internalConstants', 'Blockly.uiPosition', 'Blockly.utils.Rect', 'Blockly.utils.Size', 'Blockly.utils.Svg', 'Blockly.utils.dom'], {'lang': 'es6', 'module': 'goog'});
 goog.addDependency('../../generators/dart.js', ['Blockly.Dart'], ['Blockly.Generator', 'Blockly.inputTypes', 'Blockly.utils.string'], {'lang': 'es6'});
-goog.addDependency('../../generators/dart/colour.js', ['Blockly.Dart.colour'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/lists.js', ['Blockly.Dart.lists'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/logic.js', ['Blockly.Dart.logic'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/loops.js', ['Blockly.Dart.loops'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/math.js', ['Blockly.Dart.math'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/procedures.js', ['Blockly.Dart.procedures'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/text.js', ['Blockly.Dart.texts'], ['Blockly.Dart']);
-goog.addDependency('../../generators/dart/variables.js', ['Blockly.Dart.variables'], ['Blockly.Dart']);
+goog.addDependency('../../generators/dart/colour.js', ['Blockly.Dart.colour'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/lists.js', ['Blockly.Dart.lists'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/logic.js', ['Blockly.Dart.logic'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/loops.js', ['Blockly.Dart.loops'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/math.js', ['Blockly.Dart.math'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/procedures.js', ['Blockly.Dart.procedures'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/text.js', ['Blockly.Dart.texts'], ['Blockly.Dart'], {'lang': 'es6'});
+goog.addDependency('../../generators/dart/variables.js', ['Blockly.Dart.variables'], ['Blockly.Dart'], {'lang': 'es6'});
 goog.addDependency('../../generators/dart/variables_dynamic.js', ['Blockly.Dart.variablesDynamic'], ['Blockly.Dart', 'Blockly.Dart.variables']);
 goog.addDependency('../../generators/javascript.js', ['Blockly.JavaScript'], ['Blockly.Generator', 'Blockly.inputTypes', 'Blockly.utils.global', 'Blockly.utils.object', 'Blockly.utils.string']);
 goog.addDependency('../../generators/javascript/colour.js', ['Blockly.JavaScript.colour'], ['Blockly.JavaScript']);