feat(filterFilter): pass index to function predicate

Closes #654

Author: colincasey

src/ng/filter/filter.js

@@ -25,9 +25,9 @@
  *     property of the object. That's equivalent to the simple substring match with a `string`
  *     as described above.
  *
- *   - `function(value)`: A predicate function can be used to write arbitrary filters. The function is
- *     called for each element of `array`. The final result is an array of those elements that
- *     the predicate returned true for.
+ *   - `function(value, index)`: A predicate function can be used to write arbitrary filters. The
+ *     function is called for each element of `array`. The final result is an array of those
+ *     elements that the predicate returned true for.
  *
  * @param {function(actual, expected)|true|undefined} comparator Comparator which is used in
  *     determining if the expected value (from the filter expression) and actual value (from
@@ -120,9 +120,9 @@ function filterFilter() {
     var comparatorType = typeof(comparator),
         predicates = [];
 
-    predicates.check = function(value) {
+    predicates.check = function(value, index) {
       for (var j = 0; j < predicates.length; j++) {
-        if(!predicates[j](value)) {
+        if(!predicates[j](value, index)) {
           return false;
         }
       }
@@ -211,7 +211,7 @@ function filterFilter() {
     var filtered = [];
     for ( var j = 0; j < array.length; j++) {
       var value = array[j];
-      if (predicates.check(value)) {
+      if (predicates.check(value, j)) {
         filtered.push(value);
       }
     }

test/ng/filter/filterSpec.js

@@ -49,6 +49,16 @@ describe('Filter: filter', function() {
     expect(filter(items, function(i) {return i.done;}).length).toBe(1);
   });
 
+  it('should pass the index to a function predicate', function() {
+    var items = [0, 1, 2, 3];
+
+    var result = filter(items, function(value, index) {
+      return index % 2 === 0;
+    });
+
+    expect(result).toEqual([0, 2]);
+  });
+
   it('should take object as predicate', function() {
     var items = [{first: 'misko', last: 'hevery'},
                  {first: 'adam', last: 'abrons'}];