Module 10: Performance Tips

Performance Tip: Managing Click Delay

Problem

When beginning mobile development, you may notice that your app feels a bit sluggish when you tap on the screen. This is because the mobile web browser is trying to interpret touch commands to map them to old-style click events. The browser receives a touchstart event first, then it listens to see if the finger is going to move to scroll or release to become a tap before it fires the click event your app is listening for. These same browser engines also have a double-tap-to-zoom function so then there’s the issue of distinguishing between a tap and double tap.

The total lag introduced by the browser trying to interpret the touch event to click event mapping is about 300ms. 300ms may not sound like a lot but it’s more than enough to make an app feel noticeable lag.

Solution

Use a touch-to-click polyfill like FastClick. FastClick is a library you can implement to take the incoming touch events and maps them to the click event without the 300ms delay. An example of one way to use it is shown below, see their documentation for more details.

window.addEventListener('load', function() {
		FastClick.attach(document.body);
}, false);

Use a UI framework with built-in handling for this issue. Some also fix this issue for you out of the box such as Ionic and OnsenUI.