Allow inheriting of fromJson in fields

core/field.js

@@ -154,6 +154,15 @@ Blockly.Field = function(value, opt_validator, opt_config) {
   opt_validator && this.setValidator(opt_validator);
 };
 
+/**
+ * Construct a Field from a JSON arg object.
+ * @param {!Object} options_ A JSON object with options (options).
+ * @return {!Blockly.Field} The new field instance.
+ */
+Blockly.Field.fromJson = function(options_) {
+  throw Error("Field subclass doesn't define fromJson");
+};
+
 /**
  * The default value for this field.
  * @type {*}
@@ -276,7 +285,7 @@ Blockly.Field.prototype.configure_ = function(config) {
  */
 Blockly.Field.prototype.setSourceBlock = function(block) {
   if (this.sourceBlock_) {
-    throw Error('Field already bound to a block.');
+    throw Error('Field already bound to a block');
   }
   this.sourceBlock_ = block;
 };

core/field_angle.js

@@ -135,7 +135,9 @@ Blockly.FieldAngle.prototype.DEFAULT_VALUE = 0;
  * @nocollapse
  */
 Blockly.FieldAngle.fromJson = function(options) {
-  return new Blockly.FieldAngle(options['angle'], undefined, options);
+  // `this` might be a subclass of FieldAngle if that class doesn't override
+  // the static fromJson method.
+  return new this(options['angle'], undefined, options);
 };
 
 /**

core/field_checkbox.js

@@ -63,7 +63,9 @@ Blockly.FieldCheckbox.prototype.DEFAULT_VALUE = false;
  * @nocollapse
  */
 Blockly.FieldCheckbox.fromJson = function(options) {
-  return new Blockly.FieldCheckbox(options['checked'], undefined, options);
+  // `this` might be a subclass of FieldCheckbox if that class doesn't override
+  // the static fromJson method.
+  return new this(options['checked'], undefined, options);
 };
 
 /**

core/field_colour.js

@@ -104,7 +104,9 @@ Blockly.utils.object.inherits(Blockly.FieldColour, Blockly.Field);
  * @nocollapse
  */
 Blockly.FieldColour.fromJson = function(options) {
-  return new Blockly.FieldColour(options['colour'], undefined, options);
+  // `this` might be a subclass of FieldColour if that class doesn't override
+  // the static fromJson method.
+  return new this(options['colour'], undefined, options);
 };
 
 /**

core/field_dropdown.js

@@ -149,6 +149,8 @@ Blockly.FieldDropdown.ImageProperties;
  * @nocollapse
  */
 Blockly.FieldDropdown.fromJson = function(options) {
+  // `this` might be a subclass of FieldDropdown if that class doesn't override
+  // the static fromJson method.
   return new Blockly.FieldDropdown(options['options'], undefined, options);
 };
 

core/field_image.js

@@ -132,8 +132,9 @@ Blockly.FieldImage.prototype.DEFAULT_VALUE = '';
  * @nocollapse
  */
 Blockly.FieldImage.fromJson = function(options) {
-  return new Blockly.FieldImage(
-      options['src'], options['width'], options['height'],
+  // `this` might be a subclass of FieldImage if that class doesn't override
+  // the static fromJson method.
+  return new this(options['src'], options['width'], options['height'],
       undefined, undefined, undefined, options);
 };
 

core/field_label.js

@@ -65,7 +65,9 @@ Blockly.FieldLabel.prototype.DEFAULT_VALUE = '';
  */
 Blockly.FieldLabel.fromJson = function(options) {
   var text = Blockly.utils.replaceMessageReferences(options['text']);
-  return new Blockly.FieldLabel(text, undefined, options);
+  // `this` might be a subclass of FieldLabel if that class doesn't override
+  // the static fromJson method.
+  return new this(text, undefined, options);
 };
 
 /**

core/field_label_serializable.js

@@ -48,7 +48,9 @@ Blockly.utils.object.inherits(Blockly.FieldLabelSerializable,
  */
 Blockly.FieldLabelSerializable.fromJson = function(options) {
   var text = Blockly.utils.replaceMessageReferences(options['text']);
-  return new Blockly.FieldLabelSerializable(text, undefined, options);
+  // `this` might be a subclass of FieldLabelSerializable if that class doesn't
+  // override the static fromJson method.
+  return new this(text, undefined, options);
 };
 
 /**

core/field_multilineinput.js

@@ -89,7 +89,9 @@ Blockly.FieldMultilineInput.prototype.configure_ = function(config) {
  */
 Blockly.FieldMultilineInput.fromJson = function(options) {
   var text = Blockly.utils.replaceMessageReferences(options['text']);
-  return new Blockly.FieldMultilineInput(text, undefined, options);
+  // `this` might be a subclass of FieldLabel if that class doesn't override
+  // the static fromJson method.
+  return new this(text, undefined, options);
 };
 
 /**

core/field_number.js

@@ -91,7 +91,9 @@ Blockly.FieldNumber.prototype.DEFAULT_VALUE = 0;
  * @nocollapse
  */
 Blockly.FieldNumber.fromJson = function(options) {
-  return new Blockly.FieldNumber(options['value'],
+  // `this` might be a subclass of FieldNumber if that class doesn't override
+  // the static fromJson method.
+  return new this(options['value'],
       undefined, undefined, undefined, undefined, options);
 };
 

core/field_textinput.js

@@ -110,7 +110,9 @@ Blockly.FieldTextInput.prototype.DEFAULT_VALUE = '';
  */
 Blockly.FieldTextInput.fromJson = function(options) {
   var text = Blockly.utils.replaceMessageReferences(options['text']);
-  return new Blockly.FieldTextInput(text, undefined, options);
+  // `this` might be a subclass of FieldTextInput if that class doesn't override
+  // the static fromJson method.
+  return new this(text, undefined, options);
 };
 
 /**

core/field_variable.js

@@ -100,8 +100,9 @@ Blockly.utils.object.inherits(Blockly.FieldVariable, Blockly.FieldDropdown);
  */
 Blockly.FieldVariable.fromJson = function(options) {
   var varName = Blockly.utils.replaceMessageReferences(options['variable']);
-  return new Blockly.FieldVariable(
-      varName, undefined, undefined, undefined, options);
+  // `this` might be a subclass of FieldVariable if that class doesn't override
+  // the static fromJson method.
+  return new this(varName, undefined, undefined, undefined, options);
 };
 
 /**