PPK in the BK on Mobile JavaScript

Mobile Web, JavaScript, UI Patterns

I recently had the pleasure of seeing a true Web pioneer give a talk on mobile JavaScript. A Touching Look Into The Future Known As Today brings Peter-Paul Koch (@ppk, creator of quirksmode.org) to Brooklyn to give an updated talk about his experience in the trenches testing JavaScript touch event support on various mobile devices. I'll attempt to distill it down to some key points.

Mouse events and touch events are blended on mobile

The three interaction modes, in the order of the most to least we know about them:

  1. Mouse
  2. Keyboard
  3. Touch

Event handling on the desktop is easy because the mouse and keyboard events rarely fire simultaneously. But with the advent of touch-screen devices, both touch and mouse events fire, a conscious decision to allow mobile users to browse the countless existing sites relying on mouse events for interaction.

If you want to make a distinction:

// desktop
element.onmousedown = dostuff;

// touch
element.ontouchstart = function() {
  element.onmousedown = null;

Half-a-second delay on click

Conventional web design tells us the click event is slow because it doesn't fire until after a mousedown followed by mouseup. Some web experiences optimize for this by using mousedown. In mobile, it's even more noticeable (delay approaches 500ms). There are many possibilities once a touch starts (drag, swipe, pinch, long-press) and a delay is the only resort the OS has to determine when a click (simple one-finger touch) has happened.

Touchstart is the touch equivalent of mousedown, but bind to it at your own risk (do you know how to fine-tune interaction better than Apple?)

In short, no matter how many cores in your high-end tablet processor, you're still going to experience a noticeable delay when clicking on links (or anything livened on click) in a web experience on your device.

Use onclick to catch the long tail of mobile devices out there

If your concern is a large breadth of device support in your JavaScript, rely on the click event. Recall that this was ambiguous in the desktop world (fired by enter key and all mouse buttons) so it covered multiple cases there, too.

But also consider that touch really isn't click. There is much more information in a touch such as concurrent touches and touch area that simply vanishes when translated to a click.

What you can't (yet) do…

A lot of time was spent on the point that hover is unsupported on mobile, at least not in the way it is intended. This segues into LukeW's mobile first approach, and how this kind of thinking forces you to focus on the most important content. Maybe what's in that hover tooltip really isn't critical after all...

There is no wide support for the zoom event but it would be an interesting way to measure how readable and navigable your website is through analytics. Do users often have to zoom in on your forms or text content?

The spec (and its quirks)

Apple's guidelines for the blend of events that fire on a touch quickly became a standard adopted by all other multitouch devices:

  1. Touchstart
  2. Mouseover
  3. Mousemove (only one)
  4. Mousedown
  5. Click
  6. (Apply any hover styles)

On iOS and Symbian, if the DOM changes on mouseover to include style changes, all further events are cancelled. An example of why this is desirable is a traditional dropdown menu, as it gives you an elegant way to open the menu without risking following a top-level link.

If you touch a new element on a page, mouseout fires on the original element.

The touchmove event continues to fire after finger leaves the element firing the event.

Event delegation on iOS stops at the body element and does not reach the document element. An ugly workaround is to add an anonymous empty function to the element you want to delegate to on the appropriate event. An even weirder workaround: cursor: pointer in CSS.

Bind mousemove to the document to account for erratic movement (this is good practice on the desktop too). Contrast this with touchmove which continues to fire as you leave the element, so there's no need to listen at a higher level.

For keyboard control on drag and drop, use keydown on arrow keys

A nifty implementation of carousel in mobile: http://quirksmode.org/m/tests/scrollayer.html


Q&A focused on current trends.

Multitouch trackpads? What we know today is a 2-finger scroll fires mousewheel event. That might be the extent of touch recognition in JavaScript, because the interaction is not as direct with a trackpad.

Progressive enhancement will become mandatory. Pixel perfect styling will be prohibitive in time and cost.

Do we foresee any new touch events? Maybe a few but the current spec lets us combine touch information to describe almost any gesture. What may grow is support for the accelerometer and other sensors available on different devices.

Thanks for coming to New York, PPK! (And thanks HUGE for hosting - you might have the sweetest office space in the world).