Adding support for isElementPresent with Protractor locators.

Closes #11.

lib/protractor.js

@@ -365,6 +365,7 @@ Protractor.prototype.wrapWebElement = function(element) {
 
   var originalFindElement = element.findElement;
   var originalFindElements = element.findElements;
+  var originalIsElementPresent = element.isElementPresent;
 
   /**
    * @see webdriver.WebElement.findElement
@@ -391,6 +392,22 @@ Protractor.prototype.wrapWebElement = function(element) {
     return originalFindElements.apply(element, arguments);
   }
 
+  /**
+   * @see webdriver.WebElement.isElementPresent
+   * @return {!webdriver.promise.Promise} A promise that will be resolved with
+   *     whether an element could be located on the page.
+   */
+  element.isElementPresent = function(locator, varArgs) {
+    thisPtor.waitForAngular();
+    if (locator.findArrayOverride) {
+      return locator.findArrayOverride(element.getDriver(), element).
+          then(function (arr) {
+            return !!arr.length;
+          });
+    }
+    return originalIsElementPresent.apply(element, arguments);
+  };
+
   /**
    * Evalates the input as if it were on the scope of the current element.
    * @param {string} expression
@@ -448,6 +465,21 @@ Protractor.prototype.findElements = function(locator, varArgs) {
   return this.driver.findElements(locator, varArgs);
 };
 
+/**
+ * Tests if an element is present on the page.
+ * @see webdriver.WebDriver.isElementPresent
+ * @return {!webdriver.promise.Promise} A promise that will resolve to whether
+ *     the element is present on the page.
+ */
+Protractor.prototype.isElementPresent = function(locatorOrElement, varArgs) {
+  if (locatorOrElement.findArrayOverride) {
+    return locatorOrElement.findArrayOverride(this.driver).then(function(arr) {
+      return !!arr.length;
+    });
+  }
+  return this.driver.isElementPresent(locatorOrElement, varArgs);
+};
+
 /**
  * Add a module to load before Angular whenever Protractor.get is called.
  * Modules will be registered after existing modules already on the page,

spec/findelements_spec.js

@@ -123,6 +123,12 @@ describe('finding elements', function() {
           column('qux'));
       expect(byCol.getText()).toEqual('Wed');
     });
+
+    it('should determine if an element is present', function() {
+      expect(ptor.isElementPresent(protractor.By.binding('greet'))).toBe(true);
+      expect(ptor.isElementPresent(protractor.By.binding('nopenopenope'))).
+          toBe(false);
+    });
   });
 
   describe('further examples', function() {
@@ -204,7 +210,6 @@ describe('finding elements', function() {
 
     it('should find multiple elements scoped properly with chaining',
       function() {
-        ptor.debugger();
         ptor.findElements(protractor.By.binding('item')).then(function(elems) {
           expect(elems.length).toEqual(4);
         });
@@ -214,6 +219,16 @@ describe('finding elements', function() {
               expect(elems.length).toEqual(2);
             });
       });
+
+    it('should determine element presence properly with chaining', function() {
+      expect(ptor.findElement(protractor.By.id('baz')).
+          isElementPresent(protractor.By.binding('item.resuedBinding'))).
+          toBe(true);
+
+      expect(ptor.findElement(protractor.By.id('baz')).
+        isElementPresent(protractor.By.binding('nopenopenope'))).
+        toBe(false);
+    })
   });
 
   describe('evaluating statements', function() {