feat(protractor): implement reduce and filter for ElementArrayFinder

See #877

lib/protractor.js

@@ -327,6 +327,92 @@ var buildElementHelper = function(ptor) {
     });
   };
 
+  /**
+   * Apply a filter function to each element found using the locator. Returns 
+   * promise of a new array with all elements that pass the filter function. The
+   * filter function receives the ElementFinder as the first argument 
+   * and the index as a second arg.
+   *
+   * @alias element.all(locator).filter(filterFn)
+   * @view
+   * <ul class="items">
+   *   <li class="one">First</li>
+   *   <li class="two">Second</li>
+   *   <li class="three">Third</li>
+   * </ul>
+   *
+   * @example
+   * element.all(by.css('.items li')).filter(function(elem, index) {
+   *   return elem.getText().then(function(text) {
+   *     return text === 'Third';
+   *   });
+   * }).then(function(filteredElements) {
+   *   filteredElements[0].click();
+   * });
+   *
+   * @param {function(ElementFinder, number): webdriver.WebElement.Promise} filterFn 
+   *     Filter function that will test if an element should be returned.
+   *     filterFn should return a promise that resolves to a boolean.
+   * @return {!webdriver.promise.Promise} A promise that resolves to an array
+   *     of ElementFinders that satisfy the filter function.
+   */
+  ElementArrayFinder.prototype.filter = function(filterFn) {
+    return this.asElementFinders_().then(function(arr) {
+      var list = [];
+      arr.forEach(function(elementFinder, index) {
+        filterFn(elementFinder, index).then(function(satisfies) {
+          if (satisfies) {
+            list.push(elementFinder);
+          }
+        });
+      });
+      return list;
+    });
+  };
+
+  /**
+   * Apply a reduce function against an accumulator and every element found 
+   * using the locator (from left-to-right). The reduce function has to reduce
+   * every element into a single value (the accumulator). Returns promise of 
+   * the accumulator. The reduce function receives the accumulator, current 
+   * ElementFinder, the index, and the entire array of ElementFinders, 
+   * respectively.
+   *
+   * @alias element.all(locator).reduce(reduceFn)
+   * @view
+   * <ul class="items">
+   *   <li class="one">First</li>
+   *   <li class="two">Second</li>
+   *   <li class="three">Third</li>
+   * </ul>
+   *
+   * @example
+   * var value = element.all(by.css('.items li')).reduce(function(acc, elem) {
+   *   return elem.getText().then(function(text) {
+   *     return acc + text + ' ';
+   *   });
+   * });
+   *
+   * expect(value).toEqual('First Second Third ');
+   *
+   * @param {function(number, ElementFinder, number, Array.<ElementFinder>)} 
+   *     reduceFn Reduce function that reduces every element into a single value.
+   * @param {*} initialValue Initial value of the accumulator. 
+   * @return {!webdriver.promise.Promise} A promise that resolves to the final
+   *     value of the accumulator. 
+   */
+  ElementArrayFinder.prototype.reduce = function(reduceFn, initialValue) {
+    var valuePromise = webdriver.promise.fulfilled(initialValue);
+    return this.asElementFinders_().then(function(arr) {
+      arr.forEach(function(elementFinder, index) {
+        valuePromise = valuePromise.then(function(value) {
+          return reduceFn(value, elementFinder, index, arr);
+        });
+      });
+      return valuePromise;
+    });
+  };
+
   /**
    * The ElementFinder can be treated as a WebElement for most purposes, in 
    * particular, you may perform actions (i.e. click, getText) on them as you

spec/basic/elements_spec.js

@@ -231,6 +231,37 @@ describe('ElementFinder', function() {
     expect(labels).toEqual([1, 2, 3, 4, 5, 6, 7]);
   });
 
+  it('should filter elements', function() {
+    browser.get('index.html#/form');
+    var count = element.all(by.css('.menu li a')).filter(function(elem) {
+      return elem.getText().then(function(text) {
+        return text === 'bindings';
+      });
+    }).then(function(filteredElements) {
+      return filteredElements.length;
+    });
+
+    expect(count).toEqual(1);
+  });
+
+  it('should reduce elements', function() {
+    browser.get('index.html#/form');
+    var value = element.all(by.css('.menu li a')).
+        reduce(function(currentValue, elem, index, elemArr) {
+          return elem.getText().then(function(text) {
+            return currentValue + index + '/' + elemArr.length + ': ' + text + '\n';
+          });
+        }, '');
+
+    expect(value).toEqual('0/7: repeater\n' +
+                          '1/7: bindings\n' +
+                          '2/7: form\n' +
+                          '3/7: async\n' +
+                          '4/7: conflict\n' +
+                          '5/7: polling\n' +
+                          '6/7: animation\n');
+  });
+
   it('should export an isPresent helper', function() {
     browser.get('index.html#/form');