Attempt to work around the IE/Edge bug where getComputedTextLength() throws an exception when the SVG node is not visible. This workaround forces a re-render, which in turn, forces a re-calculation of the node width once a block is inserted into the workspace SVG. This workaround is only executed on IE and Edge. See https://groups.google.com/forum/#!topic/blockly/T8IR4t4xAIY for the initial discussion of this issue.

Author: timdawborn

core/block_render_svg.js

@@ -29,6 +29,8 @@ goog.provide('Blockly.BlockSvg.render');
 
 goog.require('Blockly.BlockSvg');
 
+goog.require('goog.userAgent');
+
 
 // UI constants for rendering blocks.
 /**
@@ -314,6 +316,13 @@ Blockly.BlockSvg.prototype.renderFields_ =
     if (!root) {
       continue;
     }
+
+    // Force a width re-calculation on IE and Edge to get around the issue
+    // described in Blockly.Field.getCachedWidth
+    if (goog.userAgent.IE || goog.userAgent.EDGE) {
+      field.updateWidth();
+    }
+
     if (this.RTL) {
       cursorX -= field.renderSep + field.renderWidth;
       root.setAttribute('transform',

core/field.js

@@ -295,6 +295,15 @@ Blockly.Field.prototype.render_ = function() {
   var textNode = document.createTextNode(this.getDisplayText_());
   this.textElement_.appendChild(textNode);
 
+  this.updateWidth();
+};
+
+/**
+ * Updates thw width of the field. This calls getCachedWidth which won't cache
+ * the approximated width on IE/Edge when `getComputedTextLength` fails. Once
+ * it eventually does succeed, the result will be cached.
+ **/
+Blockly.Field.prototype.updateWidth = function() {
   var width = Blockly.Field.getCachedWidth(this.textElement_);
   if (this.borderRect_) {
     this.borderRect_.setAttribute('width',
@@ -306,24 +315,36 @@ Blockly.Field.prototype.render_ = function() {
 /**
  * Gets the width of a text element, caching it in the process.
  * @param {!Element} textElement An SVG 'text' element.
- * @retur {number} Width of element.
+ * @return {number} Width of element.
  */
 Blockly.Field.getCachedWidth = function(textElement) {
   var key = textElement.textContent + '\n' + textElement.className.baseVal;
-  if (Blockly.Field.cacheWidths_ && Blockly.Field.cacheWidths_[key]) {
-    var width = Blockly.Field.cacheWidths_[key];
-  } else {
-    try {
-      var width = textElement.getComputedTextLength();
-    } catch (e) {
-      // MSIE 11 is known to throw "Unexpected call to method or property
-      // access." if Blockly is hidden.
-      var width = textElement.textContent.length * 8;
-    }
-    if (Blockly.Field.cacheWidths_) {
-      Blockly.Field.cacheWidths_[key] = width;
+  var width;
+
+  // Return the cached width if it exists.
+  if (Blockly.Field.cacheWidths_) {
+    width = Blockly.Field.cacheWidths_[key];
+    if (width) {
+      return width;
     }
   }
+
+  // Attempt to compute fetch the width of the SVG text element.
+  try {
+    width = textElement.getComputedTextLength();
+  } catch (e) {
+    // MSIE 11 and Edge are known to throw "Unexpected call to method or
+    // property access." if the block is hidden. Instead, use an
+    // approximation and do not cache the result. At some later point in time
+    // when the block is inserted into the visible DOM, this method will be
+    // called again and, at that point in time, will not throw an exception.
+    return textElement.textContent.length * 8;
+  }
+
+  // Cache the computed width and return.
+  if (Blockly.Field.cacheWidths_) {
+    Blockly.Field.cacheWidths_[key] = width;
+  }
   return width;
 };
 

core/xml.js

@@ -28,6 +28,7 @@ goog.provide('Blockly.Xml');
 
 goog.require('goog.asserts');
 goog.require('goog.dom');
+goog.require('goog.userAgent');
 
 
 /**
@@ -367,6 +368,11 @@ Blockly.Xml.domToBlock = function(xmlBlock, workspace) {
       setTimeout(function() {
         if (topBlock.workspace) {  // Check that the block hasn't been deleted.
           topBlock.setConnectionsHidden(false);
+          // Force a render on IE and Edge to get around the issue described in
+          // Blockly.Field.getCachedWidth
+          if (goog.userAgent.IE || goog.userAgent.EDGE) {
+            topBlock.render();
+          }
         }
       }, 1);
       topBlock.updateDisabled();