feat(tagsInput): add newTagText option

Add an option for binding to the text in the input element.
This feature is important because it allows developers to know when
the input has changed as well the state of the input at the time of
the change. An example use case is doing custom validations that
regular expressions couldn't satisfy.

Closes mbenford#197.

src/tags-input.js

@@ -9,6 +9,7 @@
  * Renders an input box with tag editing support.
  *
  * @param {string} ngModel Assignable angular expression to data-bind to.
+ * @param {string} newTagText Assignable angular expression for data-binding to the underlying input for a new tag.
  * @param {string=} [displayProperty=text] Property to be rendered as the tag label.
  * @param {string=} [type=text] Type of the input element. Only 'text', 'email' and 'url' are supported values.
  * @param {number=} tabindex Tab order of the control.
@@ -121,6 +122,7 @@ tagsInput.directive('tagsInput', function($timeout, $document, tagsInputConfig)
         require: 'ngModel',
         scope: {
             tags: '=ngModel',
+            newTagText: '=?',
             onTagAdded: '&',
             onInvalidTag: '&',
             onTagRemoved: '&'
@@ -200,6 +202,10 @@ tagsInput.directive('tagsInput', function($timeout, $document, tagsInputConfig)
 
             scope.newTag = { text: '', invalid: null };
 
+            scope.$watch('newTag.text', function(value) {
+                scope.newTagText = value;
+            });
+
             scope.getDisplayText = function(tag) {
                 return safeToString(tag[options.displayProperty]);
             };

test/tags-input.spec.js

@@ -377,6 +377,21 @@ describe('tags-input directive', function() {
         });
     });
 
+    describe('new-tag-text option', function() {
+        it('updates as text is typed into the input field', function() {
+            // Arrange
+            compile('new-tag-text="innerModel"');
+
+            // Act
+            sendKeyPress('f'.charCodeAt(0));
+            sendKeyPress('o'.charCodeAt(0));
+            sendKeyPress('o'.charCodeAt(0));
+
+            // Assert
+            expect($scope.innerModel).toEqual('foo');
+        });
+    });
+
     describe('tabindex option', function() {
         it('sets the input field tab index', function() {
             // Arrange/Act