May 25


Mar 17

Simulate mouse / touch events with jQuery in PhantomJS and the browser

For my little project jQuery Finger, I wanted to be able to continuously test it while coding. This can be easily achieved using the magic combo of Grunt, Mocha (with Chai) and PhantomJS.

I just had to launch grunt watch and listen to the evil bip telling me “test have failed, you suck nooby noob!”.

This is what I wanted, but things became more complicated when I wanted to run tests with more advanced user inputs such as tap, double tap, long tap, drag and swipe, across multiple elements.

I have tried to use MouseEvents and TouchEvent to simulate it, but I couldn’t make it work properly with PhantomJS. If somebody has successfully achieved this, I’m interested in!

The code of this article is hosted here. Use it, fork it!

jQuery is your best friend

For jQuery Finger, I must use jQuery as a direct dependency. That’s convenient I guess because jQuery has the ability to trigger events, and particulary mouse/touch events. It adds an abstraction above native events which was very handy for me.

The caveat of using jQuery to trigger events is that you must register jQuery events specifically. You can’t trigger a jQuery click and hope catching it if you registered your listener with addEventListener. jQuery simply triggers an event using its own internal sugar. If this is a blocker for you, this article might still be interesting because the global idea remains the same.

Manage your virtual pointer

So how can we try to simulate pointer events ?

We can use the magic of the document.elementFromPoint function. It tells which DOM element lives at the given position. AFAIK it is supported since quite a long time.

All we have to do, is to keep track of coordinates. When we want to trigger an event, we retreive the DOM element, and call jQuery.fn.trigger on it. Simple as pie.

Here is the first draft of our virtual pointer:

With this first version, we can easily:

A classic jQuery event is built on top of a native event that you can access with the originalEvent property. Some handy properties are directly copied to the jQuery event object.

pageX and pageY are one of these. They give the pointer absolute coordinates when the event is fired. jQuery tries to unify these properties accross every browser. But, on some mobile browsers, such as Mobile Safari, pageX and pageY stay to 0. The only trustable source for coordinates resides in the event.originalEvent.touches[0] properties.

The problem is when you manually trigger a jQuery event, it is created from scratch. So pageX, pageY and originalEvent are missing. We have to create them manually and forward our virtual pointer's coordinates.

Let’s add press and doubletap event

press event is an alias for a long tap event.

Here is the updated version of our initial virtual pointer:

The code is pretty self explanatory.

I will just explain the security multiplier. setTimeout is a cool bro, but he is not very punctual. So, if your code really depends on a time threshold, you should never put the setTimeout value to that threshold, or near it. By applying a +0.5/-0.5 security multiplier, you are always sure that you will be either on one or the other side.

Now let’s add some motion

To handle motion, we will have to pretend that the cursor is … moving, woot!

We will need destination coordinates and a duration. Our job will be to interpolate coordinates between current and destination, and call the mousemove/touchmove event at a given interval.

In real life, motion events may be triggered at a very, perhaps sometimes too high rate (i.e. *Chrome’s rate is around every 2ms).
We won’t be able to be so precise, but who cares? We will just use our good old friend setTimeout with a 0 timeout to simulate AMAP fake moves.

Here is the update:

Now, we can call move to simulate motion, and tapStart, move, tapEnd sequence to simulate some kind of drag. Great!

Let’s finish him!

With those three utility functions, we are now able to simulate gestures.

Right of the Batman, here is our final code:

That’s it! This is a basic implementation of our virtual pointer. It should allow us to simulate mouse/touch events in the browser and in PhantomJS.

As a side note, PhantomJS is detected as a touch device because window.ontouchstart is defined. This appears to be something common with some WebKit forks.

Bonus: prevent user interaction

During the simulation we don’t want any real event messing around with our tests.
Well, keep your hand away from your mouse, that’s it!

No, you can’t? Ok…

When you trigger an event with jQuery, it comes with an additional property isTrigger. So, basically, in your event handlers you can tell if this is a fake or a real event.
In our case, we are only interested in fake events, not real ones.

The only satisfying solution I found is proxying each jQuery event handlers and skipping real ones.

We could just prepend our event listeners with something like this:

But do we? Not really… Let’s use jQuery.event.special in our test environment to proxy every jQuery event handler dynamically:

Just be sure you execute this code before running your tests and registering your events. You will then be able to harlem shake your mouse / fingers without any side effect.


Everything in this article is included in the Github version, plus some additional bonuses:

Also, you can take a look at jQuery Finger :-)

Mar 02

TJ Holowaychuk: Modular CSS preprocessing with rework -


Several months ago I started a project named Rework, a very fast, simple, flexible, and modular CSS preprocessor. The biggest and most obvious question I get is how this tool compares to something like Stylus, LESS, or Sass, and why would you want to use it.

The simple answer is that…

(Source: tjholowaychuk)

Feb 25

99 Steps of Progress - Imgur -

Imgur is used to share photos with social networks and online communities, and has the funniest pictures from all over the Internet.

Feb 22

(Source: agho)

Oct 04

System V with forever for your node.js application

The alternative to its Upstart brother on a Debian system with the same use case.

Here it is: To enable your boot script:

See also

Oct 03

Upstart with forever for your node.js application

Servers reboot while you are sleeping, it happens …

So you already are using the great forever tool. No? take a look here!.
But something is missing: automatic startup of your application when the machine (re)boots.

The use case

Multiple options are available to you, and quite a lot of resources on the subject too. But I really want to focus on a tricky use case (mine):


Basically you need to set up your own Linux service. I will only focus on upstart which is a "replacement for the venerable System-V init".

As a vast majority of Linux services, you can start, stop and restart your application. These features are already provided by forever. We will only provide a way to start automatically your application. The newly crafted service will only have that purpose. To manage your application, use forever as usual.
We could probably wrap forever behaviour in the service, but this really not the aim of this article.

The upstart script

Right of the bat, here is the script:

System V with forever for your node.js application

  • Deploying Node.js With Upstart and Monit
  • Deploying node.js with Upstart
  • Running a Node.js Server as a Service Using Forever
  • Manage Linux init or startup scripts
  • Sep 28


    Sep 11


    Sep 07