DalekJS: Test if an element has focus

2 min Edit
"You cannot depend on your eyes when your imagination is out of focus."
Mark Twain,

Introducing DalekJS

We are currently making a big push at work to try and automate testing of all our front end code and try and achieve as much code coverage as possible.

Besides writing unit tests, we wanted to write UI tests to test our components and their behaviour in the browser. Selenium was an obvious candidate for this work, but we all just knew that none of us developers would want to maintain Selenium tests and run them after every change in the code.

We needed something that was quick to run, and allowed us to failed our cost fast; oh and fun to write as well! This where DalekJS comes into the picture. It has come into life when another group of very smart people went down the Selenium path and ran into a whole lot of problems before deciding to solve the problem properly and in turn creating DalekJS for all of us to use. I definitely would reccomend their “This ain’t Selenium” write-up that shares a great learning lesson for all software development teams out there.

Test for element focus in DalekJS

Anyway, so not getting into too much detail about how DalekJS should be used (that is a write-up for another time), I was writing some tests and needed a way to test if a given element on the page has focus.

DalekJS currently does not support such an assert requirement. However, DalekJS provides the powerful .execute action which allows for any JavaScript function to be executed within the browser context.

Not wanting to be dependent on any other JavaScript framework like JQuery to determine if an element selector has focus, I wrote the following helper method to test for focus by using the native document.activeElement function available in browsers from as old as IE4.

module.exports = {
    hasFocus: function(test, selector, message) {
        return test
            .execute(function(selectorParam, messageParam){
                var expectedEl = window.document.querySelector(selectorParam);
                var activeEl = window.document.activeElement;
                this.assert.ok(expectedEl === activeEl, messageParam);
            }, selector, message);

One important gotcha picked up whilst writing the code snippet above is eluded to in the DalekJS documentation when it specifies the following:

.execute - Executes a JavaScript function within the browser context

If you need to pass in a parameter to the .execute function, it cannot be done using JavaScript closure because the DalekJS (or node) context is very different than the browser context which is what is actually being used. DalekJS currently does not throw any error if the contexts are conflicting and fails silently. I’ve raised an issue about this and hopefully it will get fixed for a better developer experience.