The MutationObserver method observe() configures the MutationObserver callback to begin receiving notifications of changes to the DOM that match the given options. Depending on the configuration, the observer may watch a single Node in the DOM tree, or that node and some or all of its descendant nodes.

To stop the MutationObserver (so that none of its callbacks will be triggered any longer), call MutationObserver.disconnect().


mutationObserver.observe(target[, options])


A DOM Node (which may be an Element) within the DOM tree to watch for changes, or to be the root of a subtree of nodes to be watched.
options Optional
An optional MutationObserverInit object providing options that describe what DOM mutations should be reported to the observer's callback.

Return value



Thrown in any of the following circumstances:

Usage notes

Reusing MutationObservers

You can call observe() multiple times on the same MutationObserver to watch for changes to different parts of the DOM tree and/or different types of changes. There are some caveats to note:

  • If you call observe() on a node that's already being observed by the same MutationObserver, all existing observers are automatically removed from all targets being observed before the new observer is activated.
  • If the same MutationObserver is not already in use on the target, then the existing observers are left alone and the new one is added.

Observation follows nodes when disconnected

Mutation observers are intended to let you be able to watch the desired set of nodes over time, even if the direct connections between those nodes are severed. If you begin watching a subtree of nodes, and a portion of that subtree is detached and moved elsewhere in the DOM, you continue to watch the detached segment of nodes, receiving the same callbacks as before the nodes were detached from the original subtree.

In other words, until you've been notified that nodes are being split off from your monitored subtree, you'll get notifications of changes to that split-off subtree and its nodes. This prevents you from missing changes that occur after the connection is severed and before you have a chance to specifically begin monitoring the moved node or subtree for changes.

This means that in theory if you keep track of the MutationRecord objects describing the changes that occur, and , you should be able to "undo" the changes, rewinding the DOM back to its initial state.



Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 18 Yes 14 11 15 6
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support Yes 18 Yes 14 14 6 Yes

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.