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I am switching from Protractor to Nightwatch.js, and I am facing some difficulties with the way Nightwatch handles the promises.

To give an example, I am trying to count the number of element satisfying a given criterion. The count function is in a page object, so separated from the test itself:

The page object mand:

    countToDoList: function(browser) {
        browser.elements('css selector', "input[ng-model='todo.done']", function(result){
            return result.value.length;
        });
    }

and the call in the test:

'Angular - 1' : function(browser) {
  var angular = browser.page.angularPO();
  var mainPage = angular.section.main;

  angular.openMainPage(browser);
  var countToDoBoxes = 0;

  countToDoBoxes = mainPage.countToDoList(browser);
  console.log("countToDoBoxes = " + countToDoBoxes);

  browser.end();
}

This returns "countToDoBoxes = undefined". And based on my (short) experience with Protractor, I assume that this is due to the function not fulfilling the promise, when it's passed to "countToDoBoxes".

Is there a way to make this work?

I am switching from Protractor to Nightwatch.js, and I am facing some difficulties with the way Nightwatch handles the promises.

To give an example, I am trying to count the number of element satisfying a given criterion. The count function is in a page object, so separated from the test itself:

The page object mand:

    countToDoList: function(browser) {
        browser.elements('css selector', "input[ng-model='todo.done']", function(result){
            return result.value.length;
        });
    }

and the call in the test:

'Angular - 1' : function(browser) {
  var angular = browser.page.angularPO();
  var mainPage = angular.section.main;

  angular.openMainPage(browser);
  var countToDoBoxes = 0;

  countToDoBoxes = mainPage.countToDoList(browser);
  console.log("countToDoBoxes = " + countToDoBoxes);

  browser.end();
}

This returns "countToDoBoxes = undefined". And based on my (short) experience with Protractor, I assume that this is due to the function not fulfilling the promise, when it's passed to "countToDoBoxes".

Is there a way to make this work?

• javascript
• promise
• nightwatch.js

Share Improve this question Follow edited Nov 14, 2015 at 1:44 eppineda 68733 silver badges2020 bronze badges asked Nov 9, 2015 at 11:02 MajujMajuj 17911 silver badge1212 bronze badges 3

• 1 If you expect browser.elements to return a promise, then you should probably use .then() instead of passing the callback directly. Also, you'd obviously have to return from the countToDoList method. – Bergi Commented Nov 14, 2015 at 14:30
• Just for my own interest, why are you switching? – SuperUberDuper Commented Dec 7, 2015 at 16:11
• @SuperUberDuper : I work on a different project, and this new one works with Nightwatch.js (not my choice, and can't change that) – Majuj Commented Dec 7, 2015 at 17:29

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2 Answers 2

Sorted by: Reset to default 6

I couldn't find the API description for elements, however here is your code, modified to return a Bluebird promise. (You could do something similar with the Promise library of your choice.)

countToDoList: function(browser) {
    return new Promise(function(resolve, reject) {
        browser.elements('css selector', "input[ng-model='todo.done']", function(result){
            resolve(result.value.length);
        });

    });
}

I'm not going to answer the question you have, instead, I'll show a solution to the problem you have. I think this will help Googlers who've e here trying to use promises with Nightwatch as well.

Firstly, Nightwatch doesn't have a promise-based API, it uses callbacks. If you try to use promises with Nightwatch it'll be painful because you're moving against its programming paradigm.

So what I think should do is, firstly, modify the countToDoList function so it receives a callback function. Call it with the value you've derived.

It's also important that you return browser so we can chain something after this.

countToDoList: function(browser, callback) {
  return browser.elements('css selector', "input[ng-model='todo.done']", function(result){
    callback(result.value.length);
  });
}

Now, in your test, use the callback in countToDoList to assign a value to countToDoBoxes. You'll then need to chain the perform method. This method ensures that whatever you put in its callback is added to the end of Nightwatch's mand queue. Now you can be sure you'll have the value of countToDoBoxes available when you try to log it.

'Angular - 1' : function(browser) {
  var angular = browser.page.angularPO();
  var mainPage = angular.section.main;

  angular.openMainPage(browser);
  let countToDoBoxes;

  mainPage
    .countToDoList(browser, function(count) {
      countToDoBoxes = count;
    })
    .perform(function() {
      console.log("countToDoBoxes = " + countToDoBoxes);
    })
    .end();
}

By the way, this is all explained in the article Understanding the Command Queue which for some unknown reason is not directly in the Nightwatch docs where I think it belongs.

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