feat(ngPluralize): add support for count to be a one-time expression

Closes #10004

src/ng/directive/ngPluralize.js

@@ -173,7 +173,9 @@
     </example>
  */
 var ngPluralizeDirective = ['$locale', '$interpolate', function($locale, $interpolate) {
-  var BRACE = /{}/g;
+  var BRACE = /{}/g,
+      IS_WHEN = /^when(Minus)?(.+)$/;
+
   return {
     restrict: 'EA',
     link: function(scope, element, attr) {
@@ -184,34 +186,44 @@ var ngPluralizeDirective = ['$locale', '$interpolate', function($locale, $interp
           whensExpFns = {},
           startSymbol = $interpolate.startSymbol(),
           endSymbol = $interpolate.endSymbol(),
-          isWhen = /^when(Minus)?(.+)$/;
+          braceReplacement = startSymbol + numberExp + '-' + offset + endSymbol,
+          watchRemover = angular.noop,
+          lastCount;
 
       forEach(attr, function(expression, attributeName) {
-        if (isWhen.test(attributeName)) {
-          whens[lowercase(attributeName.replace('when', '').replace('Minus', '-'))] =
-            element.attr(attr.$attr[attributeName]);
+        var tmpMatch = IS_WHEN.exec(attributeName);
+        if (tmpMatch) {
+          var whenKey = (tmpMatch[1] ? '-' : '') + lowercase(tmpMatch[2]);
+          whens[whenKey] = element.attr(attr.$attr[attributeName]);
         }
       });
       forEach(whens, function(expression, key) {
-        whensExpFns[key] =
-          $interpolate(expression.replace(BRACE, startSymbol + numberExp + '-' +
-            offset + endSymbol));
+        whensExpFns[key] = $interpolate(expression.replace(BRACE, braceReplacement));
+
       });
 
-      scope.$watch(function ngPluralizeWatch() {
-        var value = parseFloat(scope.$eval(numberExp));
+      scope.$watch(numberExp, function ngPluralizeWatchAction(newVal) {
+        var count = parseFloat(newVal);
+        var countIsNaN = isNaN(count);
 
-        if (!isNaN(value)) {
-          //if explicit number rule such as 1, 2, 3... is defined, just use it. Otherwise,
-          //check it against pluralization rules in $locale service
-          if (!(value in whens)) value = $locale.pluralCat(value - offset);
-           return whensExpFns[value](scope);
-        } else {
-          return '';
+        if (!countIsNaN && !(count in whens)) {
+          // If an explicit number rule such as 1, 2, 3... is defined, just use it.
+          // Otherwise, check it against pluralization rules in $locale service.
+          count = $locale.pluralCat(count - offset);
+        }
+
+        // If both `count` and `lastCount` are NaN, we don't need to re-register a watch.
+        // In JS `NaN !== NaN`, so we have to exlicitly check.
+        if ((count !== lastCount) && !(countIsNaN && isNaN(lastCount))) {
+          watchRemover();
+          watchRemover = scope.$watch(whensExpFns[count], updateElementText);
+          lastCount = count;
         }
-      }, function ngPluralizeWatchAction(newVal) {
-        element.text(newVal);
       });
+
+      function updateElementText(newText) {
+        element.text(newText || '');
+      }
     }
   };
 }];

test/ng/directive/ngPluralizeSpec.js

@@ -242,4 +242,76 @@ describe('ngPluralize', function() {
       });
     });
   });
+
+
+  describe('bind-once', function() {
+
+    it('should support for `count` to be a one-time expression',
+      inject(function($compile, $rootScope) {
+        element = $compile(
+            '<ng:pluralize count="::email"' +
+                           "when=\"{'one': 'You have one new email'," +
+                                   "'other': 'You have {} new emails'}\">" +
+            '</ng:pluralize>')($rootScope);
+        elementAlt = $compile(
+            '<ng:pluralize count="::email" ' +
+                           "when-one='You have one new email' " +
+                           "when-other='You have {} new emails'>" +
+            '</ng:pluralize>')($rootScope);
+
+        $rootScope.email = undefined;
+        $rootScope.$digest();
+        expect(element.text()).toBe('');
+        expect(elementAlt.text()).toBe('');
+
+        $rootScope.email = 3;
+        $rootScope.$digest();
+        expect(element.text()).toBe('You have 3 new emails');
+        expect(elementAlt.text()).toBe('You have 3 new emails');
+
+        $rootScope.email = 2;
+        $rootScope.$digest();
+        expect(element.text()).toBe('You have 3 new emails');
+        expect(elementAlt.text()).toBe('You have 3 new emails');
+
+        $rootScope.email = 1;
+        $rootScope.$digest();
+        expect(element.text()).toBe('You have 3 new emails');
+        expect(elementAlt.text()).toBe('You have 3 new emails');
+      })
+    );
+
+
+    it('should still update other embedded expressions',
+      inject(function($compile, $rootScope) {
+        element = $compile(
+            '<ng:pluralize count="::email"' +
+                           "when=\"{'one': 'You, {{user}}, have one new email'," +
+                                   "'other': 'You, {{user}}, have {} new emails'}\">" +
+            '</ng:pluralize>')($rootScope);
+        elementAlt = $compile(
+            '<ng:pluralize count="::email" ' +
+                           "when-one='You, {{user}}, have one new email' " +
+                           "when-other='You, {{user}}, have {} new emails'>" +
+            '</ng:pluralize>')($rootScope);
+
+        $rootScope.user = 'Lucas';
+        $rootScope.email = undefined;
+        $rootScope.$digest();
+        expect(element.text()).toBe('');
+        expect(elementAlt.text()).toBe('');
+
+        $rootScope.email = 3;
+        $rootScope.$digest();
+        expect(element.text()).toBe('You, Lucas, have 3 new emails');
+        expect(elementAlt.text()).toBe('You, Lucas, have 3 new emails');
+
+        $rootScope.user = 'Pete';
+        $rootScope.email = 2;
+        $rootScope.$digest();
+        expect(element.text()).toBe('You, Pete, have 3 new emails');
+        expect(elementAlt.text()).toBe('You, Pete, have 3 new emails');
+      })
+    );
+  });
 });