mutant.js

"The only constant is change" -- Splinter

Get told about DOM mutations and other events which will affect layout.

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Why mutant.js?

Sometimes you need to know when the layout of an HTML element has changed.

For example, on Gitter we have popover components in which the size of the popover may change as new content is added or removed.

Another place we need this is in order to support reverse scrolling. If the user is scrolled to the bottom of a screen and new content arrives, the scroll viewport should be adjusted down to track the "bottom". Likewise, when new content arrives above the top of the viewport, the scroll must be adjusted so that the users view is maintained and does not jump.

Because we use external and user supplied content, including oembed and images, it's not always possible to know exactly when the DOM will change.

Using a timer is inefficient and the user's experience will be jumpy.

How to use it

git clone [email protected]:gitterHQ/mutant.js.git

cd mutant.js

make

Then include public/assets/mutant.js in your browser application.

Dependencies

None. Nada. Nil.

API

function layout() {
  /* Recenter your popover here, or adjust your scroll, etc etc */
}

var div = document.querySelector('.my-div');
var mutant = new Mutant(div, layout);

/* If you make a change and dont want to be notified of it, call takeRecords */
setTimeout(function() {
  div.appendChild(document.createElement('SPAN'));
  mutant.takeRecords(); // Now you wont be notified of the span event.
}, 10);

/* Sometime later, when you're done. Call disconnect */
mutant.disconnect();

By default only childList and subtree are being observed as mutation properties, but you can specify your own options as a third argument.

var options = {
  observers: {
    childList: true, // listen to div's child elements additions or removals, default: true
    subtree: false, // don't listen to div's descendants mutations, default: true
    attributres: true // also listen to div's attributes updates, default: false
  }
}
var mutant = new Mutant(div, layout, options);

All available mutation properties and their descriptions are listed on MDN.

Responding to transitionend events

Mutant.js can optionally also fire events at the end of a CSS3 transition sequence. By default this will not happen but can be useful to notify of mutations that occur over a duration of time.

Enable support for transition events using the transitions:true option, like so

var options = {
  transitions: true
}

var mutant = new Mutant(div, layout, options);

Using mutantjs to detect reflow events

If you are using mutant.js to detect events which will trigger a reflow, you can optimise your configuration to ignore specific transitionend events. For example opacity events will not trigger a reflow, so can therefore be ignored. Specify a blacklist of css properties to ignore transitionend events in the Mutant constructor using the ignoreTransitions property as follows:

function layout() {
  // Do something here
}

var mutant = new Mutant(div, layout, options, {
  transitions: true,
  ignoreTransitions: ['opacity'], // Opacity will never trigger a reflow...
});

Receiving periodic notifications during a transition

Unfortunately there is no easy way to detect the start of a transition in the DOM, although this may change. Until there is, you can only get transition events at the end of the transition.

If you wish to receive period events during the transition, in order to make the user experience smoother, you can tell Mutant.js to expect a transition using startTransition and endTransition.

Start a transition

startTransition(element, maxTimeMs) element the element which will be involved in the transition maxTimeMs (optional) is the maximum time the transition will occur for, in ms

End a transition

Note that endTransition is not needed if maxTimeMs is used in the startTransition call. endTransition(element, maxTimeMs) element the element which was involved in the transition

Example:

function doAnimation() {
  var el = document.querySelector(...);
  mutant.startTransition(element, 100)
}

License

The MIT License (MIT)

Copyright (c) 2014

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.