fix(ngModel): process input type=number according to convention, using valueAsNumber

lib/directive/ng_model.dart

@@ -211,12 +211,17 @@ class InputTextLikeDirective {
  *
  *     <input type="number|range" ng-model="myModel">
  *
- * This creates a two-way binding between a number-based input element
- * so long as the ng-model attribute is present on the input element. Whenever
- * the value of the input element changes then the matching model property on the
- * scope will be updated as well as the other way around (when the scope property
- * is updated).
- *
+ * Model:
+ * 
+ *     num myModel;
+ * 
+ * This creates a two-way binding between the input and the named model property
+ * (e.g., myModel in the example above). When processing the input, its value is
+ * read as a [num], via the [dom.InputElement.valueAsNumber] field. If the input
+ * text does not represent a number, then the model is appropriately set to
+ * [double.NAN]. Setting the model property to [null] will clear the input.
+ * Setting the model to [double.NAN] will have no effect (input will be left
+ * unchanged).
  */
 @NgDirective(selector: 'input[type=number][ng-model]')
 @NgDirective(selector: 'input[type=range][ng-model]')
@@ -225,17 +230,34 @@ class InputNumberLikeDirective {
   final NgModel ngModel;
   final Scope scope;
 
+  num get typedValue => inputElement.valueAsNumber;
+  void set typedValue(num value) {
+    // [chalin, 2014-02-16] This post 
+    // http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2010-January/024829.html
+    // suggests that setting `valueAsNumber` to null should clear the field, but
+    // it does not. [TODO: put BUG/ISSUE number here].  We implement a
+    // workaround by setting `value`. Clean-up once the bug is fixed.
+    if (value == null) {
+      inputElement.value = null;
+    } else { 
+      inputElement.valueAsNumber = value;
+    }
+  }
+
   InputNumberLikeDirective(dom.Element this.inputElement, this.ngModel, this.scope) {
     ngModel.render = (value) {
-      inputElement.value = value == null ? '' : value.toString();
+      if (value != typedValue 
+          && (value == null || value is num && !value.isNaN)) {
+        typedValue = value;
+      }
     };
     inputElement
         ..onChange.listen(relaxFnArgs(processValue))
         ..onInput.listen(relaxFnArgs(processValue));
   }
 
   processValue() {
-    var value = num.parse(inputElement.value, (_) => null);
+    num value = typedValue;
     if (value != ngModel.viewValue) {
       ngModel.dirty = true;
       scope.$apply(() => ngModel.viewValue = value);

test/directive/ng_model_spec.dart

@@ -109,7 +109,65 @@ describe('ng-model', () {
     }));
   });
 
+  /* An input of type number can only have assigned to its [value] field
+   * a string that represents a valid number. Any attempts to assign
+   * any other string will have no effect on the [value] field.
+   * 
+   * This function simulates typing the given string value into the input
+   * field regardless of whether it represents a valid number or not. It
+   * has the side-effect of setting the window focus to the input.
+   */
+  void setNumberInputValue(InputElement input, String value) {
+    input..focus()
+      ..dispatchEvent(new TextEvent('textInput', data: value));
+  }
+
   describe('type="number" like', () {
+
+    it('should leave input unchanged when text does not represent a valid number', inject((Injector i) {
+      var modelFieldName = 'modelForNumFromInvalid1';
+      var element = _.compile('<input type="number" ng-model="$modelFieldName">');
+      dom.querySelector('body').append(element);
+
+      // Subcase: text not representing a valid number.
+      var piX = '3.141x';
+      setNumberInputValue(element, piX);
+      // Because the text is not a valid number, the element value is empty.
+      expect(element.value).toEqual('');
+      // But the selection can confirm that the text is there:
+      element.selectionStart = 0;
+      element.selectionEnd = piX.length;
+      expect(dom.window.getSelection().toString()).toEqual(piX);
+      // When the input is invalid, the model is [double.NAN]:
+      _.triggerEvent(element, 'change');
+      expect(_.rootScope[modelFieldName].isNaN).toBeTruthy();
+
+      // Subcase: text representing a valid number (as if the user had erased
+      // the trailing 'x').
+      num pi = 3.14159;
+      setNumberInputValue(element, pi.toString());
+      _.triggerEvent(element, 'change');
+      expect(element.value).toEqual(pi.toString());
+      expect(_.rootScope[modelFieldName]).toEqual(pi);
+    }));
+
+    it('should not reformat user input to equivalent numeric representation', inject((Injector i) {
+      var modelFieldName = 'modelForNumFromInvalid2';
+      var element = _.compile('<input type="number" ng-model="$modelFieldName">');
+      dom.querySelector('body').append(element);
+
+      var ten = '1e1';
+      setNumberInputValue(element, ten);      
+      _.triggerEvent(element, 'change');
+      expect(_.rootScope[modelFieldName]).toEqual(10);
+      // Ensure that the input text is literally the same
+      element.selectionStart = 0;
+      // Set the selectionEnd to one beyond ten.length in
+      // case angular added some extra text.
+      element.selectionEnd = ten.length + 1;
+      expect(dom.window.getSelection().toString()).toEqual(ten);
+    }));
+
     it('should update input value from model', inject(() {
       _.compile('<input type="number" ng-model="model">');
       _.rootScope.$digest();
@@ -142,15 +200,15 @@ describe('ng-model', () {
       expect(_.rootScope.model).toEqual(43);
     }));
 
-    it('should update model to null from a blank input value', inject(() {
+    it('should update model to NaN from a blank input value', inject(() {
       _.compile('<input type="number" ng-model="model" probe="p">');
       Probe probe = _.rootScope.p;
       var ngModel = probe.directive(NgModel);
       InputElement inputElement = probe.element;
 
       inputElement.value = '';
       _.triggerEvent(inputElement, 'change');
-      expect(_.rootScope.model).toBeNull();
+      expect(_.rootScope.model.isNaN).toBeTruthy();
     }));
 
     it('should update model from the input value for range inputs', inject(() {