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PointerEvents Polyfill: a unified event system for the web platform

branch: stable
README.md

Learn the tech

Why Pointer Events?

Mouse events and Touch events are fundamentally different beasts in browsers today, and that makes it hard to write cross-platform apps.

For example, a simple finger paint app needs plenty of work to behave correctly with mouse and touch:

Current platforms that implement touch events also provide mouse events for backward compatibility; however, only a subset of mouse events are fired and the semantics are changed.

  • Mouse events are only fired after the touch sequence ends.
  • Mouse events are not fired on elements without a click event handler. One must be attached by default, or directly on the element with “onclick”.
  • Click events are not fired if the content of the page changes in a mousemove or mouseover event.
  • Click events are fired 300ms after the touch sequence ends.
  • More information: Apple Developer Documentation.

Additionally, Touch events are sent only to the element that received the touchstart. This is fundamentally different than mouse events, which fire on the element that is under the mouse. To make them behave similarly, touch events need to be retargeted with document.elementFromPoint.

These incompatibilities lead to applications having to listen to 2 sets of events, mouse on desktop and touch for mobile.

This forked interaction experience is cumbersome and hard to maintain.

Instead, there should exist a set of events that are normalized such that they behave exactly the same, no matter the source: touch, mouse, stylus, skull implant, etc. To do this right, this normalized event system needs to be available for all the web platform to use.

Thus, PointerEvents!

Basic Usage

By default, no PointerEvents are sent from an element. This maximizes possibility that a browser can deliver smooth scrolling and jank-free gestures. If you want to receive events, you must set the touch-action property of that element.

  1. Set up some elements to create events with the touch-action attribute

    • <div id="not-a-scroller" touch-action="none"></div>
      • Generates events all the time, will not scroll
    • <div id="horizontal-scroller" touch-action="pan-x">
      • Generates events in the y axis, scrolls in the x axis
    • <div id="vertical-scroller" touch-action="pan-y">
      • Generates events in the x axis, scrolls in the y axis
    • <div id="all-axis-scroller" touch-action="pan-x pan-y">
      • Generates events only when tapping, scrolls otherwise
      • Can also have the value pan-y pan-x or scroll
  2. Listen for the desired events

    • pointermove: a pointer moves, similar to touchmove or mousemove.
    • pointerdown: a pointer is activated, or a device button held.
    • pointerup: a pointer is deactivated, or a device button released.
    • pointerover: a pointer has moved onto an element.
    • pointerout: a pointer is no longer on an element it once was.
    • pointerenter: a pointer enters the bounding box of an element.
    • pointerleave: a pointer leaves the bounding box of an element.
    • pointercancel: a pointer will no longer generate events.
  3. As elements come and go, or have their touch-action attribute changed, they will send the proper set of PointerEvents.

Polyfill Details

Getting Started

  1. Place the loader script in the document head
    • <script src="PointerEvents/src/pointerevents.js"></script>
  2. Set up your event listeners
  3. You're Done!

Where can I use PointerEvents?

PointerEvents should work on all "Evergreen" (self-updating) browsers.

It has been tested on Chrome, Safari, Firefox, Opera, and IE 10.

Polyfill Limitations

touch-action

According to the spec, the touch-action css property determines if an element will receive PointerEvents. Specifically, only elements with the styling that have the touch-action value of none will receive events.

Due to the difficult nature of polyfilling new CSS properties, this library will use a touch-action attribute instead. In addition, run time changes involving the touch-action attribute will be monitored for maximum flexibility.

Touches will not generate events unless inside of an area that has a valid touch-action defined that is not auto. This is to maintain compositiong scrolling optimizations where possible.

Browser Compatibility

Full Support

Chrome 18+, Safari 6+, IE 10, Firefox 14+

Partial Support

Opera 12+, does not support changes to touch-action attribute, nor added or removed elements

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