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
clickevent handler. One must be attached by default, or directly on the element withonclick. clickevents are not fired if the content of the page changes in amousemoveormouseoverevent.clickevents 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, Pointer Events!
By default, no Pointer Events 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.
- Set up some elements to create events with the
touch-actionattribute
<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-xorscroll
- 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.
- As elements come and go, or have their
touch-actionattribute changed, they will send the proper set of Pointer Events.
- Place the PEP script in the document head
<script src="https://code.jquery.com/pep/0.3.0/pep.js"></script>
- Set up your event listeners
- You're done!
Check out some of the samples at http://jquery.github.io/PEP/.
According to the spec, the touch-action css property controls whether an element will perform a "default action" such as scrolling, or receive a continuous stream of Pointer 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 attribute defined. This is to maintain compositiong scrolling optimizations where possible.
PEP should work on IE 10+ and the latest versions of Chrome, Safari, Firefox, and Opera.