diff --git a/blocks/lists.js b/blocks/lists.js
index b8d91c56a..79cae676f 100644
--- a/blocks/lists.js
+++ b/blocks/lists.js
@@ -819,7 +819,7 @@ Blockly.Blocks['lists_split'] = {
       } else if (mode == 'JOIN') {
         return Blockly.Msg['LISTS_SPLIT_TOOLTIP_JOIN'];
       }
-      throw 'Unknown mode: ' + mode;
+      throw Error('Unknown mode: ' + mode);
     });
   },
   /**
diff --git a/blocks/logic.js b/blocks/logic.js
index 0d8f72111..01f4e55b6 100644
--- a/blocks/logic.js
+++ b/blocks/logic.js
@@ -381,7 +381,7 @@ Blockly.Constants.Logic.CONTROLS_IF_MUTATOR_MIXIN = {
           elseStatementConnection = clauseBlock.statementConnection_;
           break;
         default:
-          throw 'Unknown block type.';
+          throw TypeError('Unknown block type: ' + clauseBlock.type);
       }
       clauseBlock = clauseBlock.nextConnection &&
           clauseBlock.nextConnection.targetBlock();
@@ -419,7 +419,7 @@ Blockly.Constants.Logic.CONTROLS_IF_MUTATOR_MIXIN = {
               inputDo && inputDo.connection.targetConnection;
           break;
         default:
-          throw 'Unknown block type.';
+          throw TypeError('Unknown block type: ' + clauseBlock.type);
       }
       clauseBlock = clauseBlock.nextConnection &&
           clauseBlock.nextConnection.targetBlock();
diff --git a/blocks/procedures.js b/blocks/procedures.js
index 7241dcf50..562bde00f 100644
--- a/blocks/procedures.js
+++ b/blocks/procedures.js
@@ -627,7 +627,7 @@ Blockly.Blocks['procedures_callnoreturn'] = {
       return;
     }
     if (paramIds.length != paramNames.length) {
-      throw 'Error: paramNames and paramIds must be the same length.';
+      throw RangeError('paramNames and paramIds must be the same length.');
     }
     this.setCollapsed(false);
     if (!this.quarkIds_) {
diff --git a/generators/dart/lists.js b/generators/dart/lists.js
index 42552713c..dd2a493e4 100644
--- a/generators/dart/lists.js
+++ b/generators/dart/lists.js
@@ -243,7 +243,7 @@ Blockly.Dart['lists_getIndex'] = function(block) {
         break;
     }
   }
-  throw 'Unhandled combination (lists_getIndex).';
+  throw Error('Unhandled combination (lists_getIndex).');
 };
 
 Blockly.Dart['lists_setIndex'] = function(block) {
@@ -323,7 +323,7 @@ Blockly.Dart['lists_setIndex'] = function(block) {
       }
       break;
   }
-  throw 'Unhandled combination (lists_setIndex).';
+  throw Error('Unhandled combination (lists_setIndex).');
 };
 
 Blockly.Dart['lists_getSublist'] = function(block) {
@@ -348,7 +348,7 @@ Blockly.Dart['lists_getSublist'] = function(block) {
         var at1 = '0';
         break;
       default:
-        throw 'Unhandled option (lists_getSublist).';
+        throw Error('Unhandled option (lists_getSublist).');
     }
     switch (where2) {
       case 'FROM_START':
@@ -363,7 +363,7 @@ Blockly.Dart['lists_getSublist'] = function(block) {
         // There is no second index if LAST option is chosen.
         break;
       default:
-        throw 'Unhandled option (lists_getSublist).';
+        throw Error('Unhandled option (lists_getSublist).');
     }
     if (where2 == 'LAST') {
       var code = list + '.sublist(' + at1 + ')';
@@ -445,7 +445,7 @@ Blockly.Dart['lists_split'] = function(block) {
     }
     var functionName = 'join';
   } else {
-    throw 'Unknown mode: ' + mode;
+    throw Error('Unknown mode: ' + mode);
   }
   var code = input + '.' + functionName + '(' + delimiter + ')';
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
diff --git a/generators/dart/loops.js b/generators/dart/loops.js
index 0dd7c0ce5..6c83a2fd5 100644
--- a/generators/dart/loops.js
+++ b/generators/dart/loops.js
@@ -159,5 +159,5 @@ Blockly.Dart['controls_flow_statements'] = function(block) {
     case 'CONTINUE':
       return 'continue;\n';
   }
-  throw 'Unknown flow statement.';
+  throw Error('Unknown flow statement.');
 };
diff --git a/generators/dart/math.js b/generators/dart/math.js
index 867822beb..c37df0ea3 100644
--- a/generators/dart/math.js
+++ b/generators/dart/math.js
@@ -160,7 +160,7 @@ Blockly.Dart['math_single'] = function(block) {
       code = 'Math.atan(' + arg + ') / Math.PI * 180';
       break;
     default:
-      throw 'Unknown math operator: ' + operator;
+      throw Error('Unknown math operator: ' + operator);
   }
   return [code, Blockly.Dart.ORDER_MULTIPLICATIVE];
 };
@@ -426,7 +426,7 @@ Blockly.Dart['math_on_list'] = function(block) {
       code = functionName + '(' + list + ')';
       break;
     default:
-      throw 'Unknown operator: ' + func;
+      throw Error('Unknown operator: ' + func);
   }
   return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
 };
diff --git a/generators/dart/text.js b/generators/dart/text.js
index 94c60f74b..589b1093b 100644
--- a/generators/dart/text.js
+++ b/generators/dart/text.js
@@ -136,7 +136,7 @@ Blockly.Dart['text_charAt'] = function(block) {
       code = functionName + '(' + text + ')';
       return [code, Blockly.Dart.ORDER_UNARY_POSTFIX];
   }
-  throw 'Unhandled option (text_charAt).';
+  throw Error('Unhandled option (text_charAt).');
 };
 
 Blockly.Dart['text_getSubstring'] = function(block) {
@@ -164,7 +164,7 @@ Blockly.Dart['text_getSubstring'] = function(block) {
         var at1 = '0';
         break;
       default:
-        throw 'Unhandled option (text_getSubstring).';
+        throw Error('Unhandled option (text_getSubstring).');
     }
     switch (where2) {
       case 'FROM_START':
@@ -178,7 +178,7 @@ Blockly.Dart['text_getSubstring'] = function(block) {
       case 'LAST':
         break;
       default:
-        throw 'Unhandled option (text_getSubstring).';
+        throw Error('Unhandled option (text_getSubstring).');
     }
     if (where2 == 'LAST') {
       var code = text + '.substring(' + at1 + ')';
diff --git a/generators/javascript/lists.js b/generators/javascript/lists.js
index d9075953f..8ab563503 100644
--- a/generators/javascript/lists.js
+++ b/generators/javascript/lists.js
@@ -170,7 +170,7 @@ Blockly.JavaScript['lists_getIndex'] = function(block) {
       }
       break;
   }
-  throw 'Unhandled combination (lists_getIndex).';
+  throw Error('Unhandled combination (lists_getIndex).');
 };
 
 Blockly.JavaScript['lists_setIndex'] = function(block) {
@@ -247,7 +247,7 @@ Blockly.JavaScript['lists_setIndex'] = function(block) {
       }
       break;
   }
-  throw 'Unhandled combination (lists_setIndex).';
+  throw Error('Unhandled combination (lists_setIndex).');
 };
 
 /**
@@ -295,7 +295,7 @@ Blockly.JavaScript['lists_getSublist'] = function(block) {
         var at1 = '0';
         break;
       default:
-        throw 'Unhandled option (lists_getSublist).';
+        throw Error('Unhandled option (lists_getSublist).');
     }
     switch (where2) {
       case 'FROM_START':
@@ -310,7 +310,7 @@ Blockly.JavaScript['lists_getSublist'] = function(block) {
         var at2 = list + '.length';
         break;
       default:
-        throw 'Unhandled option (lists_getSublist).';
+        throw Error('Unhandled option (lists_getSublist).');
     }
     code = list + '.slice(' + at1 + ', ' + at2 + ')';
   } else {
@@ -387,7 +387,7 @@ Blockly.JavaScript['lists_split'] = function(block) {
     }
     var functionName = 'join';
   } else {
-    throw 'Unknown mode: ' + mode;
+    throw Error('Unknown mode: ' + mode);
   }
   var code = input + '.' + functionName + '(' + delimiter + ')';
   return [code, Blockly.JavaScript.ORDER_FUNCTION_CALL];
diff --git a/generators/javascript/loops.js b/generators/javascript/loops.js
index 1a2ade593..416bbc8be 100644
--- a/generators/javascript/loops.js
+++ b/generators/javascript/loops.js
@@ -171,5 +171,5 @@ Blockly.JavaScript['controls_flow_statements'] = function(block) {
     case 'CONTINUE':
       return 'continue;\n';
   }
-  throw 'Unknown flow statement.';
+  throw Error('Unknown flow statement.');
 };
diff --git a/generators/javascript/math.js b/generators/javascript/math.js
index 0bd265af2..191e7af1e 100644
--- a/generators/javascript/math.js
+++ b/generators/javascript/math.js
@@ -32,7 +32,7 @@ goog.require('Blockly.JavaScript');
 Blockly.JavaScript['math_number'] = function(block) {
   // Numeric value.
   var code = parseFloat(block.getFieldValue('NUM'));
-  var order = code >= 0 ? Blockly.JavaScript.ORDER_ATOMIC : 
+  var order = code >= 0 ? Blockly.JavaScript.ORDER_ATOMIC :
               Blockly.JavaScript.ORDER_UNARY_NEGATION;
   return [code, order];
 };
@@ -140,7 +140,7 @@ Blockly.JavaScript['math_single'] = function(block) {
       code = 'Math.atan(' + arg + ') / Math.PI * 180';
       break;
     default:
-      throw 'Unknown math operator: ' + operator;
+      throw Error('Unknown math operator: ' + operator);
   }
   return [code, Blockly.JavaScript.ORDER_DIVISION];
 };
@@ -357,7 +357,7 @@ Blockly.JavaScript['math_on_list'] = function(block) {
       code = functionName + '(' + list + ')';
       break;
     default:
-      throw 'Unknown operator: ' + func;
+      throw Error('Unknown operator: ' + func);
   }
   return [code, Blockly.JavaScript.ORDER_FUNCTION_CALL];
 };
diff --git a/generators/javascript/text.js b/generators/javascript/text.js
index 9e2a375a2..357ca3eb9 100644
--- a/generators/javascript/text.js
+++ b/generators/javascript/text.js
@@ -137,7 +137,7 @@ Blockly.JavaScript['text_charAt'] = function(block) {
       var code = functionName + '(' + text + ')';
       return [code, Blockly.JavaScript.ORDER_FUNCTION_CALL];
   }
-  throw 'Unhandled option (text_charAt).';
+  throw Error('Unhandled option (text_charAt).');
 };
 
 /**
@@ -186,7 +186,7 @@ Blockly.JavaScript['text_getSubstring'] = function(block) {
         var at1 = '0';
         break;
       default:
-        throw 'Unhandled option (text_getSubstring).';
+        throw Error('Unhandled option (text_getSubstring).');
     }
     switch (where2) {
       case 'FROM_START':
@@ -201,7 +201,7 @@ Blockly.JavaScript['text_getSubstring'] = function(block) {
         var at2 = text + '.length';
         break;
       default:
-        throw 'Unhandled option (text_getSubstring).';
+        throw Error('Unhandled option (text_getSubstring).');
     }
     code = text + '.slice(' + at1 + ', ' + at2 + ')';
   } else {
diff --git a/generators/lua/lists.js b/generators/lua/lists.js
index 6b9fe006e..bdb89baf6 100644
--- a/generators/lua/lists.js
+++ b/generators/lua/lists.js
@@ -358,7 +358,7 @@ Blockly.Lua['lists_split'] = function(block) {
     }
     functionName = 'table.concat';
   } else {
-    throw 'Unknown mode: ' + mode;
+    throw Error('Unknown mode: ' + mode);
   }
   var code = functionName + '(' + input + ', ' + delimiter + ')';
   return [code, Blockly.Lua.ORDER_HIGH];
diff --git a/generators/lua/loops.js b/generators/lua/loops.js
index 785398ff7..d671534a6 100644
--- a/generators/lua/loops.js
+++ b/generators/lua/loops.js
@@ -162,5 +162,5 @@ Blockly.Lua['controls_flow_statements'] = function(block) {
     case 'CONTINUE':
       return Blockly.Lua.CONTINUE_STATEMENT;
   }
-  throw 'Unknown flow statement.';
+  throw Error('Unknown flow statement.');
 };
diff --git a/generators/lua/math.js b/generators/lua/math.js
index b60d023da..eefcee4ae 100644
--- a/generators/lua/math.js
+++ b/generators/lua/math.js
@@ -123,7 +123,7 @@ Blockly.Lua['math_single'] = function(block) {
       code = 'math.deg(math.atan(' + arg + '))';
       break;
     default:
-      throw 'Unknown math operator: ' + operator;
+      throw Error('Unknown math operator: ' + operator);
   }
   return [code, Blockly.Lua.ORDER_HIGH];
 };
@@ -383,7 +383,7 @@ Blockly.Lua['math_on_list'] = function(block) {
       break;
 
     default:
-      throw 'Unknown operator: ' + func;
+      throw Error('Unknown operator: ' + func);
   }
   return [functionName + '(' + list + ')', Blockly.Lua.ORDER_HIGH];
 };
diff --git a/generators/lua/text.js b/generators/lua/text.js
index 8a2ac914a..8f6c9467e 100644
--- a/generators/lua/text.js
+++ b/generators/lua/text.js
@@ -149,7 +149,7 @@ Blockly.Lua['text_charAt'] = function(block) {
       } else if (where == 'FROM_END') {
         var start = '-' + at;
       } else {
-        throw 'Unhandled option (text_charAt).';
+        throw Error('Unhandled option (text_charAt).');
       }
     }
     if (start.match(/^-?\w*$/)) {
@@ -185,7 +185,7 @@ Blockly.Lua['text_getSubstring'] = function(block) {
   } else if (where1 == 'FROM_END') {
     var start = '-' + at1;
   } else {
-    throw 'Unhandled option (text_getSubstring)';
+    throw Error('Unhandled option (text_getSubstring)');
   }
 
   // Get end index.
@@ -200,7 +200,7 @@ Blockly.Lua['text_getSubstring'] = function(block) {
   } else if (where2 == 'FROM_END') {
     var end = '-' + at2;
   } else {
-    throw 'Unhandled option (text_getSubstring)';
+    throw Error('Unhandled option (text_getSubstring)');
   }
   var code = 'string.sub(' + text + ', ' + start + ', ' + end + ')';
   return [code, Blockly.Lua.ORDER_HIGH];
diff --git a/generators/php/lists.js b/generators/php/lists.js
index 3fd261695..47262d6a5 100644
--- a/generators/php/lists.js
+++ b/generators/php/lists.js
@@ -255,7 +255,7 @@ Blockly.PHP['lists_getIndex'] = function(block) {
       }
       break;
   }
-  throw 'Unhandled combination (lists_getIndex).';
+  throw Error('Unhandled combination (lists_getIndex).');
 };
 
 Blockly.PHP['lists_setIndex'] = function(block) {
@@ -355,7 +355,7 @@ Blockly.PHP['lists_setIndex'] = function(block) {
       }
       break;
   }
-  throw 'Unhandled combination (lists_setIndex).';
+  throw Error('Unhandled combination (lists_setIndex).');
 };
 
 Blockly.PHP['lists_getSublist'] = function(block) {
@@ -383,7 +383,7 @@ Blockly.PHP['lists_getSublist'] = function(block) {
         var at1 = '0';
         break;
       default:
-        throw 'Unhandled option (lists_getSublist).';
+        throw Error('Unhandled option (lists_getSublist).');
     }
     switch (where2) {
       case 'FROM_START':
@@ -416,7 +416,7 @@ Blockly.PHP['lists_getSublist'] = function(block) {
         }
         break;
       default:
-        throw 'Unhandled option (lists_getSublist).';
+        throw Error('Unhandled option (lists_getSublist).');
     }
     code = 'array_slice(' + list + ', ' + at1 + ', ' + length + ')';
   } else {
@@ -497,7 +497,7 @@ Blockly.PHP['lists_split'] = function(block) {
     }
     var functionName = 'implode';
   } else {
-    throw 'Unknown mode: ' + mode;
+    throw Error('Unknown mode: ' + mode);
   }
   var code = functionName + '(' + value_delim + ', ' + value_input + ')';
   return [code, Blockly.PHP.ORDER_FUNCTION_CALL];
diff --git a/generators/php/loops.js b/generators/php/loops.js
index f306b1053..b504740ba 100644
--- a/generators/php/loops.js
+++ b/generators/php/loops.js
@@ -160,5 +160,5 @@ Blockly.PHP['controls_flow_statements'] = function(block) {
     case 'CONTINUE':
       return 'continue;\n';
   }
-  throw 'Unknown flow statement.';
+  throw Error('Unknown flow statement.');
 };
diff --git a/generators/php/math.js b/generators/php/math.js
index ef9419603..5100d0f4b 100644
--- a/generators/php/math.js
+++ b/generators/php/math.js
@@ -32,7 +32,7 @@ goog.require('Blockly.PHP');
 Blockly.PHP['math_number'] = function(block) {
   // Numeric value.
   var code = parseFloat(block.getFieldValue('NUM'));
-  var order = code >= 0 ? Blockly.PHP.ORDER_ATOMIC : 
+  var order = code >= 0 ? Blockly.PHP.ORDER_ATOMIC :
               Blockly.PHP.ORDER_UNARY_NEGATION;
   if (code == Infinity) {
     code = 'INF';
@@ -139,7 +139,7 @@ Blockly.PHP['math_single'] = function(block) {
       code = 'atan(' + arg + ') / pi() * 180';
       break;
     default:
-      throw 'Unknown math operator: ' + operator;
+      throw Error('Unknown math operator: ' + operator);
   }
   return [code, Blockly.PHP.ORDER_DIVISION];
 };
@@ -321,7 +321,7 @@ Blockly.PHP['math_on_list'] = function(block) {
       code = functionName + '(' + list + ')';
       break;
     default:
-      throw 'Unknown operator: ' + func;
+      throw Error('Unknown operator: ' + func);
   }
   return [code, Blockly.PHP.ORDER_FUNCTION_CALL];
 };
diff --git a/generators/php/text.js b/generators/php/text.js
index 7903d31e7..4eeead148 100644
--- a/generators/php/text.js
+++ b/generators/php/text.js
@@ -152,7 +152,7 @@ Blockly.PHP['text_charAt'] = function(block) {
       code = functionName + '(' + text + ')';
       return [code, Blockly.PHP.ORDER_FUNCTION_CALL];
   }
-  throw 'Unhandled option (text_charAt).';
+  throw Error('Unhandled option (text_charAt).');
 };
 
 Blockly.PHP['text_getSubstring'] = function(block) {
diff --git a/generators/python/lists.js b/generators/python/lists.js
index 3d29acf22..657e44d1d 100644
--- a/generators/python/lists.js
+++ b/generators/python/lists.js
@@ -183,7 +183,7 @@ Blockly.Python['lists_getIndex'] = function(block) {
       }
       break;
   }
-  throw 'Unhandled combination (lists_getIndex).';
+  throw Error('Unhandled combination (lists_getIndex).');
 };
 
 Blockly.Python['lists_setIndex'] = function(block) {
@@ -254,7 +254,7 @@ Blockly.Python['lists_setIndex'] = function(block) {
         }
       break;
   }
-  throw 'Unhandled combination (lists_setIndex).';
+  throw Error('Unhandled combination (lists_setIndex).');
 };
 
 Blockly.Python['lists_getSublist'] = function(block) {
@@ -277,7 +277,7 @@ Blockly.Python['lists_getSublist'] = function(block) {
       var at1 = '';
       break;
     default:
-      throw 'Unhandled option (lists_getSublist)';
+      throw Error('Unhandled option (lists_getSublist)');
   }
   switch (where2) {
     case 'FROM_START':
@@ -298,7 +298,7 @@ Blockly.Python['lists_getSublist'] = function(block) {
       var at2 = '';
       break;
     default:
-      throw 'Unhandled option (lists_getSublist)';
+      throw Error('Unhandled option (lists_getSublist)');
   }
   var code = list + '[' + at1 + ' : ' + at2 + ']';
   return [code, Blockly.Python.ORDER_MEMBER];
@@ -349,7 +349,7 @@ Blockly.Python['lists_split'] = function(block) {
         Blockly.Python.ORDER_MEMBER) || '\'\'';
     var code = value_delim + '.join(' + value_input + ')';
   } else {
-    throw 'Unknown mode: ' + mode;
+    throw Error('Unknown mode: ' + mode);
   }
   return [code, Blockly.Python.ORDER_FUNCTION_CALL];
 };
diff --git a/generators/python/loops.js b/generators/python/loops.js
index 3cb1ab900..918bcdfb5 100644
--- a/generators/python/loops.js
+++ b/generators/python/loops.js
@@ -207,5 +207,5 @@ Blockly.Python['controls_flow_statements'] = function(block) {
     case 'CONTINUE':
       return 'continue\n';
   }
-  throw 'Unknown flow statement.';
+  throw Error('Unknown flow statement.');
 };
diff --git a/generators/python/math.js b/generators/python/math.js
index a2595e00c..f1307d71a 100644
--- a/generators/python/math.js
+++ b/generators/python/math.js
@@ -147,7 +147,7 @@ Blockly.Python['math_single'] = function(block) {
       code = 'math.atan(' + arg + ') / math.pi * 180';
       break;
     default:
-      throw 'Unknown math operator: ' + operator;
+      throw Error('Unknown math operator: ' + operator);
   }
   return [code, Blockly.Python.ORDER_MULTIPLICATIVE];
 };
@@ -342,7 +342,7 @@ Blockly.Python['math_on_list'] = function(block) {
       code = 'random.choice(' + list + ')';
       break;
     default:
-      throw 'Unknown operator: ' + func;
+      throw Error('Unknown operator: ' + func);
   }
   return [code, Blockly.Python.ORDER_FUNCTION_CALL];
 };
diff --git a/generators/python/text.js b/generators/python/text.js
index 0fefc77d9..2ff767b14 100644
--- a/generators/python/text.js
+++ b/generators/python/text.js
@@ -140,7 +140,7 @@ Blockly.Python['text_charAt'] = function(block) {
       code = functionName + '(' + text + ')';
       return [code, Blockly.Python.ORDER_FUNCTION_CALL];
   }
-  throw 'Unhandled option (text_charAt).';
+  throw Error('Unhandled option (text_charAt).');
 };
 
 Blockly.Python['text_getSubstring'] = function(block) {
@@ -163,7 +163,7 @@ Blockly.Python['text_getSubstring'] = function(block) {
       var at1 = '';
       break;
     default:
-      throw 'Unhandled option (text_getSubstring)';
+      throw Error('Unhandled option (text_getSubstring)');
   }
   switch (where2) {
     case 'FROM_START':
@@ -184,7 +184,7 @@ Blockly.Python['text_getSubstring'] = function(block) {
       var at2 = '';
       break;
     default:
-      throw 'Unhandled option (text_getSubstring)';
+      throw Error('Unhandled option (text_getSubstring)');
   }
   var code = text + '[' + at1 + ' : ' + at2 + ']';
   return [code, Blockly.Python.ORDER_MEMBER];