diff --git a/core/events/events_block_base.js b/core/events/events_block_base.js
index c1c0ebb61..2ba798689 100644
--- a/core/events/events_block_base.js
+++ b/core/events/events_block_base.js
@@ -51,7 +51,7 @@ Blockly.utils.object.inherits(Blockly.Events.BlockBase,
  * @return {!Object} JSON representation.
  */
 Blockly.Events.BlockBase.prototype.toJson = function() {
-  var json = Blockly.Events.BlockBase.superClass_.toJson.call(this);
+  const json = Blockly.Events.BlockBase.superClass_.toJson.call(this);
   json['blockId'] = this.blockId;
   return json;
 };
diff --git a/core/events/events_block_change.js b/core/events/events_block_change.js
index 82868aac2..6938712b0 100644
--- a/core/events/events_block_change.js
+++ b/core/events/events_block_change.js
@@ -54,7 +54,7 @@ Blockly.Events.BlockChange.prototype.type = Blockly.Events.BLOCK_CHANGE;
  * @return {!Object} JSON representation.
  */
 Blockly.Events.BlockChange.prototype.toJson = function() {
-  var json = Blockly.Events.BlockChange.superClass_.toJson.call(this);
+  const json = Blockly.Events.BlockChange.superClass_.toJson.call(this);
   json['element'] = this.element;
   if (this.name) {
     json['name'] = this.name;
@@ -89,8 +89,8 @@ Blockly.Events.BlockChange.prototype.isNull = function() {
  * @param {boolean} forward True if run forward, false if run backward (undo).
  */
 Blockly.Events.BlockChange.prototype.run = function(forward) {
-  var workspace = this.getEventWorkspace_();
-  var block = workspace.getBlockById(this.blockId);
+  const workspace = this.getEventWorkspace_();
+  const block = workspace.getBlockById(this.blockId);
   if (!block) {
     console.warn("Can't change non-existent block: " + this.blockId);
     return;
@@ -99,16 +99,17 @@ Blockly.Events.BlockChange.prototype.run = function(forward) {
     // Close the mutator (if open) since we don't want to update it.
     block.mutator.setVisible(false);
   }
-  var value = forward ? this.newValue : this.oldValue;
+  const value = forward ? this.newValue : this.oldValue;
   switch (this.element) {
-    case 'field':
-      var field = block.getField(this.name);
+    case 'field': {
+      const field = block.getField(this.name);
       if (field) {
         field.setValue(value);
       } else {
         console.warn("Can't set non-existent field: " + this.name);
       }
       break;
+    }
     case 'comment':
       block.setCommentText(/** @type {string} */ (value) || null);
       break;
@@ -121,19 +122,21 @@ Blockly.Events.BlockChange.prototype.run = function(forward) {
     case 'inline':
       block.setInputsInline(!!value);
       break;
-    case 'mutation':
-      var oldMutation = '';
+    case 'mutation': {
+      let oldMutation = '';
       if (block.mutationToDom) {
-        var oldMutationDom = block.mutationToDom();
+        const oldMutationDom = block.mutationToDom();
         oldMutation = oldMutationDom && Blockly.Xml.domToText(oldMutationDom);
       }
       if (block.domToMutation) {
-        var dom = Blockly.Xml.textToDom(/** @type {string} */ (value) || '<mutation/>');
+        const dom = Blockly.Xml.textToDom(/** @type {string} */
+            (value) || '<mutation/>');
         block.domToMutation(dom);
       }
       Blockly.Events.fire(new Blockly.Events.BlockChange(
           block, 'mutation', null, oldMutation, value));
       break;
+    }
     default:
       console.warn('Unknown change type: ' + this.element);
   }
diff --git a/core/events/events_block_create.js b/core/events/events_block_create.js
index 301068afe..119f9c0a8 100644
--- a/core/events/events_block_create.js
+++ b/core/events/events_block_create.js
@@ -58,7 +58,7 @@ Blockly.Events.BlockCreate.prototype.type = Blockly.Events.BLOCK_CREATE;
  * @return {!Object} JSON representation.
  */
 Blockly.Events.BlockCreate.prototype.toJson = function() {
-  var json = Blockly.Events.BlockCreate.superClass_.toJson.call(this);
+  const json = Blockly.Events.BlockCreate.superClass_.toJson.call(this);
   json['xml'] = Blockly.Xml.domToText(this.xml);
   json['ids'] = this.ids;
   if (!this.recordUndo) {
@@ -85,14 +85,15 @@ Blockly.Events.BlockCreate.prototype.fromJson = function(json) {
  * @param {boolean} forward True if run forward, false if run backward (undo).
  */
 Blockly.Events.BlockCreate.prototype.run = function(forward) {
-  var workspace = this.getEventWorkspace_();
+  const workspace = this.getEventWorkspace_();
   if (forward) {
-    var xml = Blockly.utils.xml.createElement('xml');
+    const xml = Blockly.utils.xml.createElement('xml');
     xml.appendChild(this.xml);
     Blockly.Xml.domToWorkspace(xml, workspace);
   } else {
-    for (var i = 0, id; (id = this.ids[i]); i++) {
-      var block = workspace.getBlockById(id);
+    for (let i = 0; i < this.ids.length; i++) {
+      const id = this.ids[i];
+      const block = workspace.getBlockById(id);
       if (block) {
         block.dispose(false);
       } else if (id == this.blockId) {
diff --git a/core/events/events_block_delete.js b/core/events/events_block_delete.js
index 38d1d6345..120ac7ddc 100644
--- a/core/events/events_block_delete.js
+++ b/core/events/events_block_delete.js
@@ -62,7 +62,7 @@ Blockly.Events.BlockDelete.prototype.type = Blockly.Events.BLOCK_DELETE;
  * @return {!Object} JSON representation.
  */
 Blockly.Events.BlockDelete.prototype.toJson = function() {
-  var json = Blockly.Events.BlockDelete.superClass_.toJson.call(this);
+  const json = Blockly.Events.BlockDelete.superClass_.toJson.call(this);
   json['oldXml'] = Blockly.Xml.domToText(this.oldXml);
   json['ids'] = this.ids;
   if (!this.recordUndo) {
@@ -89,10 +89,11 @@ Blockly.Events.BlockDelete.prototype.fromJson = function(json) {
  * @param {boolean} forward True if run forward, false if run backward (undo).
  */
 Blockly.Events.BlockDelete.prototype.run = function(forward) {
-  var workspace = this.getEventWorkspace_();
+  const workspace = this.getEventWorkspace_();
   if (forward) {
-    for (var i = 0, id; (id = this.ids[i]); i++) {
-      var block = workspace.getBlockById(id);
+    for (let i = 0; i < this.ids.length; i++) {
+      const id = this.ids[i];
+      const block = workspace.getBlockById(id);
       if (block) {
         block.dispose(false);
       } else if (id == this.blockId) {
@@ -101,7 +102,7 @@ Blockly.Events.BlockDelete.prototype.run = function(forward) {
       }
     }
   } else {
-    var xml = Blockly.utils.xml.createElement('xml');
+    const xml = Blockly.utils.xml.createElement('xml');
     xml.appendChild(this.oldXml);
     Blockly.Xml.domToWorkspace(xml, workspace);
   }
diff --git a/core/events/events_block_move.js b/core/events/events_block_move.js
index d3121e115..4318e443e 100644
--- a/core/events/events_block_move.js
+++ b/core/events/events_block_move.js
@@ -39,7 +39,7 @@ Blockly.Events.BlockMove = function(opt_block) {
     this.recordUndo = false;
   }
 
-  var location = this.currentLocation_();
+  const location = this.currentLocation_();
   this.oldParentId = location.parentId;
   this.oldInputName = location.inputName;
   this.oldCoordinate = location.coordinate;
@@ -57,7 +57,7 @@ Blockly.Events.BlockMove.prototype.type = Blockly.Events.BLOCK_MOVE;
  * @return {!Object} JSON representation.
  */
 Blockly.Events.BlockMove.prototype.toJson = function() {
-  var json = Blockly.Events.BlockMove.superClass_.toJson.call(this);
+  const json = Blockly.Events.BlockMove.superClass_.toJson.call(this);
   if (this.newParentId) {
     json['newParentId'] = this.newParentId;
   }
@@ -83,7 +83,7 @@ Blockly.Events.BlockMove.prototype.fromJson = function(json) {
   this.newParentId = json['newParentId'];
   this.newInputName = json['newInputName'];
   if (json['newCoordinate']) {
-    var xy = json['newCoordinate'].split(',');
+    const xy = json['newCoordinate'].split(',');
     this.newCoordinate =
         new Blockly.utils.Coordinate(Number(xy[0]), Number(xy[1]));
   }
@@ -96,7 +96,7 @@ Blockly.Events.BlockMove.prototype.fromJson = function(json) {
  * Record the block's new location.  Called after the move.
  */
 Blockly.Events.BlockMove.prototype.recordNew = function() {
-  var location = this.currentLocation_();
+  const location = this.currentLocation_();
   this.newParentId = location.parentId;
   this.newInputName = location.inputName;
   this.newCoordinate = location.coordinate;
@@ -109,13 +109,13 @@ Blockly.Events.BlockMove.prototype.recordNew = function() {
  * @private
  */
 Blockly.Events.BlockMove.prototype.currentLocation_ = function() {
-  var workspace = this.getEventWorkspace_();
-  var block = workspace.getBlockById(this.blockId);
-  var location = {};
-  var parent = block.getParent();
+  const workspace = this.getEventWorkspace_();
+  const block = workspace.getBlockById(this.blockId);
+  const location = {};
+  const parent = block.getParent();
   if (parent) {
     location.parentId = parent.id;
-    var input = parent.getInputWithBlock(block);
+    const input = parent.getInputWithBlock(block);
     if (input) {
       location.inputName = input.name;
     }
@@ -140,16 +140,16 @@ Blockly.Events.BlockMove.prototype.isNull = function() {
  * @param {boolean} forward True if run forward, false if run backward (undo).
  */
 Blockly.Events.BlockMove.prototype.run = function(forward) {
-  var workspace = this.getEventWorkspace_();
-  var block = workspace.getBlockById(this.blockId);
+  const workspace = this.getEventWorkspace_();
+  const block = workspace.getBlockById(this.blockId);
   if (!block) {
     console.warn("Can't move non-existent block: " + this.blockId);
     return;
   }
-  var parentId = forward ? this.newParentId : this.oldParentId;
-  var inputName = forward ? this.newInputName : this.oldInputName;
-  var coordinate = forward ? this.newCoordinate : this.oldCoordinate;
-  var parentBlock = null;
+  const parentId = forward ? this.newParentId : this.oldParentId;
+  const inputName = forward ? this.newInputName : this.oldInputName;
+  const coordinate = forward ? this.newCoordinate : this.oldCoordinate;
+  let parentBlock;
   if (parentId) {
     parentBlock = workspace.getBlockById(parentId);
     if (!parentBlock) {
@@ -161,14 +161,14 @@ Blockly.Events.BlockMove.prototype.run = function(forward) {
     block.unplug();
   }
   if (coordinate) {
-    var xy = block.getRelativeToSurfaceXY();
+    const xy = block.getRelativeToSurfaceXY();
     block.moveBy(coordinate.x - xy.x, coordinate.y - xy.y);
   } else {
-    var blockConnection = block.outputConnection || block.previousConnection;
-    var parentConnection;
-    var connectionType = blockConnection.type;
+    const blockConnection = block.outputConnection || block.previousConnection;
+    let parentConnection;
+    const connectionType = blockConnection.type;
     if (inputName) {
-      var input = parentBlock.getInput(inputName);
+      const input = parentBlock.getInput(inputName);
       if (input) {
         parentConnection = input.connection;
       }