A polyfill for the MutationObserver API (can I use?). The polyfill is more cause we can than should (with subtree at any rate)... It's async and uses a recursive timeout fallback (default checks changes every 30ms + runtime) instead of using the deprecated DOM3 MutationEvents so theoretically can support virtually any environment.
$ npm install mutationobserver-shim $ bower install MutationObserver-shim
Polyfill differences from standard interface
- Implemented using a recursive
setTimeout(every ~30 ms) rather than using a
setImmediatepolyfill; so calls will be made less frequently and likely with more data than the standard MutationObserver. In addition, it can miss changes that occur and then are lost in the interval window.
- Setting an observed elements html using
childListobserver listeners with several mutations with only 1 addedNode or removed node per mutation. With the standard you would have 1 call with multiple nodes in addedNodes and removedNodes node lists.
subtreechanges in node order (eg first element gets swapped with last) should fire a
removedNodemutation but the correct node may not always be identified.
removedNodesare arrays instead of
oldValueis always called with attribute changes
previousSiblingcorrectfullness is questionable (hard to know if the order of appended items). I'd suggest not relying on them anyway (my tests are extremely permissive with these attributes)
Supported MutationObserverInit properties
Currently supports the following MutationObserverInit properties:
- childList: Set to truthy if mutations to target's immediate children are to be observed.
- subtree: Set to truthy to do deep scans on a target's children.
- attributes: Set to truthy if mutations to target's children are to be observed. As explained in #4, the
styleattribute may not be matched in ie<8.
- attributeFilter: Set to an array of attribute local names (without namespace) if not all attribute mutations need to be observed.
- attributeOldValue: doesn't do anything attributes are always called with old value
- characterData: currently follows Mozilla's implementation in that it will only watch
textNodesvalues and not, like in webkit, where setting .innerHTML will add a characterData mutation.
By default, the polyfill will check observed nodes about 25 times per second (30 ms interval) for mutations. Try running these jsperf.com tests and the JSLitmus tests in the test suite for usage performance tests. It may be worthwile to adapt
MutationObserver._period based on UA or heuristics (todo).
From my tests observing any size element without
subtree enabled is relatively cheap. Although I've optimized the subtree check to the best of my abilities it can be costly on large trees. You can draw your own conclusions based on the JSLitmus and jsperf tests noting that you can expect the
mo to do its check 28+ times a second (by default).
Although supported, I'd recommend against watching
attributes on the
subtree on large structures, as the check is complex and expensive on terrible hardware like my phone :(
The included minified file has been tuned for performance.
I've tested and verified compatibility in the following browsers + these Sauce browsers
- Internet Explorer 8 (emulated), 9, 10 in win7 and win8
- Firefox 4, 21, 24, 26 in OSX, win7 and win8
- Opera 11.8, 12.16 in win7
- "Internet" on Android HTC One V
- Blackberry 6.0.16
Try running the test suite and see some simple example usage:
- http://jsbin.com/suqewogone listen to images being appended dynamically
- http://jsbin.com/bapohopuwi autoscroll an element as new content is added
See http://dev.opera.com/articles/view/mutation-observers-tutorial/ for some sample usage.