Fez Vrasta Fez Vrasta - 1 year ago 89
Javascript Question

Take screenshot from Karma while running tests in PhantomJS 2?

I need a way to take a screenshot during a test which uses QUnit and Karma to run inside PhantomJS 2.0.1

I've found this command:


That doesn't throw any error but doesn't seem to work, or at least, I don't know where to look for the taken screenshot.

Any clue?

Answer Source

Found a way!


I had to edit my custom PhantomJS custom launcher adding an option:

PhantomJSCustom: {
    base: 'PhantomJS',
    options: {
        onCallback: function(data){
            if (data.type === "render") {
                // this function will not have the scope of karma.conf.js so we must define any global variable inside it
                if (window.renderId === undefined) { window.renderId = 0; }
                page.render(data.fname || ("screenshot_" + (window.renderId++) + ".png"));

As you can see, we are defining the onCallback option, it will be injected inside the script launched by phantomjs. The script, then, will contain:

page.onCallback = <our function>

Now, we are able to use callPhantom to ask PhantomJS to run the content of our onCallback function and use all the native PhantomJS methods.


Now, you can use in your tests the function:

window.top.callPhantom({type: 'render'});

To take a screenshot that will be saved in the root directory of your application.

Additionally, if you define the fname you'll be able to define a custom path and file name to your screenshot.

window.top.callPhantom({type: 'render', fname: '/tmp/myscreen.png'});

Pack all together for ease of use

I've created an handy function to use inside my tests. The onCallback function is reduced to the minimum necessary, in this way all the logic is managed inside my test environment:


PhantomJSCustom: {
    base: 'PhantomJS',
    options: {
        onCallback: function(data){
            if (data.type === 'render' && data.fname !== undefined) {


// With this function you can take screenshots in PhantomJS!
// by default, screenshots will be saved in .tmp/screenshots/ folder with a progressive name (n.png)
var renderId = 0;
function takeScreenshot(file) {
    // check if we are in PhantomJS
    if (window.top.callPhantom === undefined) return;

    var options = {type: 'render'};
    // if the file argument is defined, we'll save the file in the path defined eg: `fname: '/tmp/myscreen.png'
    // otherwise we'll save it in the default directory with a progressive name
    options.fname = file || '.tmp/screenshots/' + (renderId++) + '.png';

    // this calls the onCallback function of PhantomJS, the type: 'render' will trigger the screenshot script


I got this script from this answer, adapted it and found by myself where to put it to make it work with karma.

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