fix(ExpectedConditions): allow ExpectedConditions to handle missing elements

Expected conditions used `presenceOf` and `visibilityOf` to check that it's
referencing elements which actually exist on the page, but there is a race
condition with this strategy: an element could disappear after the
`presenceOf`/`visibilityOf` check but before other checks, causing an error
to be thrown.  This PR handles this race condition in two ways:

1. `ElementFinder`'s `isEnabled`, `isDisplayed`, and `isSelected` functions now
   return false if no such element exists, rahter than throwing an error
2. `ExpectedConditions`'s `textToBePresent` and `textToBePresentInElementValue`
   now check for errors and also return false in those cases

This is a general solution to the problem referenced in
#3777 and
#3958.

Author: sjelin

lib/element.ts

@@ -17,6 +17,9 @@ let WEB_ELEMENT_FUNCTIONS = [
   'getLocation', 'isEnabled', 'isSelected', 'submit', 'clear', 'isDisplayed', 'getId', 'serialize',
   'takeScreenshot'
 ] as (keyof WebdriverWebElement)[];
+let FALSE_IF_MISSING_WEB_ELEMENT_FUNCTIONS = [
+  'isEnabled', 'isSelected', 'isDisplayed'
+] as (keyof WebdriverWebElement)[];
 
 /**
  * ElementArrayFinder is used for operations on an array of elements (as opposed
@@ -82,7 +85,8 @@ export class ElementArrayFinder extends WebdriverWebElement {
   constructor(
       public browser_: ProtractorBrowser,
       public getWebElements: () => wdpromise.Promise<WebElement[]> = null, public locator_?: any,
-      public actionResults_: wdpromise.Promise<any> = null) {
+      public actionResults_: wdpromise.Promise<any> = null,
+      public falseIfMissing_: boolean) {
     super();
 
     // TODO(juliemr): might it be easier to combine this with our docs and just
@@ -92,7 +96,8 @@ export class ElementArrayFinder extends WebdriverWebElement {
         let actionFn = (webElem: any) => {
           return webElem[fnName].apply(webElem, args);
         };
-        return this.applyAction_(actionFn);
+        return this.applyAction_(actionFn,
+            FALSE_IF_MISSING_WEB_ELEMENT_FUNCTIONS.indexOf(fnName) !== -1);
       };
     });
   }
@@ -458,8 +463,8 @@ export class ElementArrayFinder extends WebdriverWebElement {
    * @private
    */
   // map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): U[];
-  private applyAction_(actionFn: (value: WebElement, index: number, array: WebElement[]) => any):
-      ElementArrayFinder {
+  private applyAction_(actionFn: (value: WebElement, index: number, array: WebElement[]) => any,
+      falseIfMissing: boolean): ElementArrayFinder {
     let callerError = new Error();
     let actionResults = this.getWebElements()
                             .then((arr: any) => wdpromise.all(arr.map(actionFn)))
@@ -474,7 +479,8 @@ export class ElementArrayFinder extends WebdriverWebElement {
                               }
                               throw noSuchErr;
                             });
-    return new ElementArrayFinder(this.browser_, this.getWebElements, this.locator_, actionResults);
+    return new ElementArrayFinder(this.browser_, this.getWebElements, this.locator_, actionResults,
+        falseIfMissing);
   }
 
   /**
@@ -801,7 +807,14 @@ export class ElementFinder extends WebdriverWebElement {
       // Access the underlying actionResult of ElementFinder.
       this.then =
           (fn: (value: any) => any | wdpromise.IThenable<any>, errorFn?: (error: any) => any) => {
-            return this.elementArrayFinder_.then((actionResults: any) => {
+            return this.elementArrayFinder_.then(null, (error) => {
+              if (elementArrayFinder_.falseIfMissing_ &&
+                  (error instanceof wderror.NoSuchElementError)) {
+                return false;
+              } else {
+                throw error;
+              }
+            }).then((actionResults: any) => {
               if (!fn) {
                 return actionResults[0];
               }

lib/expectedConditions.ts

@@ -210,7 +210,7 @@ export class ProtractorExpectedConditions {
         // MSEdge does not properly remove newlines, which causes false
         // negatives
         return actualText.replace(/\r?\n|\r/g, '').indexOf(text) > -1;
-      });
+      }, () => false);
     };
     return this.and(this.presenceOf(elementFinder), hasText);
   }
@@ -235,7 +235,7 @@ export class ProtractorExpectedConditions {
     let hasText = () => {
       return elementFinder.getAttribute('value').then((actualText: string): boolean => {
         return actualText.indexOf(text) > -1;
-      });
+      }, () => false);
     };
     return this.and(this.presenceOf(elementFinder), hasText);
   }
@@ -388,15 +388,7 @@ export class ProtractorExpectedConditions {
    *     representing whether the element is visible.
    */
   visibilityOf(elementFinder: ElementFinder): Function {
-    return this.and(this.presenceOf(elementFinder), () => {
-      return elementFinder.isDisplayed().then((displayed: boolean) => displayed, (err: any) => {
-        if (err instanceof wderror.NoSuchElementError) {
-          return false;
-        } else {
-          throw err;
-        }
-      });
-    });
+    return this.and(this.presenceOf(elementFinder), elementFinder.isDisplayed.bind(elementFinder));
   }
 
   /**