Simulate mouse / touch events with jQuery in PhantomJS and the browser
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
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:
- change the position of the pointer with
- simulate a
- simulate a
touchstart touchendby calling
tap, assuming we register events with
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.
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,
pageY stay to
0. The only trustable source for coordinates resides in the
The problem is when you manually trigger a jQuery event, it is created from scratch. So
originalEvent are missing. We have to create them manually and forward our virtual pointer's coordinates.
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
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
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
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:
- an example of Mocha integration in the very simple test suite.
- the possibility to specify a custom scope for callbacks.
- the possibility to auto reset coordinates on each
Also, you can take a look at jQuery Finger :-)
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:
- Remove the
.shextension from the gist.
- Move it into the
- Make it executable by running
sudo chmod 755 /etc/init.d/service.
- Register the script for (re)boot by running
update-rc.d service defaults.
Upstart with forever for your node.js application
Servers reboot while you are sleeping, it happens …
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):
- You want to use forever to daemonize, manage and monitor your application.
- You want something simple to start automatically your application when the server (re)boots.
- Your application is located in the home directory of a dedicated user.
- It does not run on the port 80.
- You don’t want to start it as super user.
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: