Swingpant's Game Lab

Using removeChild to clear off a few in-game elements I noticed a bit of lag when testing on some devices so thought I’d better have a look at what the fastest removal methods are.

The three methods I selected to test were removeChild, display=”none” and a simple hide the element offscreen. Again, testing has been carried out at JSPerf.com.

My first test was on Chrome 16 and the results were pretty conclusive. display=”none” was very slow, and hide the element was by far the fastest – over 4 times faster than display=”none”.

So, conclusive proof – I should just hide my elements off the screen.

Err, no. I next tested Firefox 9.0.1. Ah, here removeChild was 2.5 times faster than both display=”none” and hiding the elements.

IE7.0 then. display=”none” and the hiding elements method were nearly 3 times faster than removeChild.

What about devices?
With Android 2.2 (Galaxy Tab 1) display=”none” was the fastest method, but only marginally so over the other two.

Safari on iPad #1 (4.2.1) flips the results on their head again with removeChild() being nearly 3 times quicker than the other two.

So how do we interpret this data? A chief decision to make would be what the target devices are. Then choose the quickest method. If we wanted a more generic approach then a series of conditionals would allow for all three methods to be present, using the most relevant one for the current browser.

For the prototypes I am working on, number one target is the iPad. A lot of my focus has been on trying to avoid using the Canvas element (entirely due to horrible performance on Android with it).

Element removal.

The (very simple) code used is here (for simplicity’s sake I use the inverse method as well to bring the element back onto the stage for subsequent removal):

var testDIV = document.createElement(‘div’);
testDIV.innerHTML = “Hello World”;

function displayIsNone()
{
testDIV.style.display=”block”;
testDIV.style.display=”none”;
}

function removeChild()
{
document.body.appendChild(testDIV);
document.body.removeChild(testDIV);
}

function moveVideo()
{
testDIV.style.left=”10px”;
testDIV.style.left=”-9999px”;
}

Try the tests yourself here: http://jsperf.com/removing-an-element-from-the-screen/3.