MutationObserver

The MutationObserver interface provides the ability to watch for changes being made to the DOM tree. It is designed as a replacement for the older Mutation Events feature which was part of the DOM3 Events specification.

Constructor

MutationObserver()

Creates and returns a new MutationObserver which will invoke a specified callback function when DOM changes occur.

Methods

disconnect()

Stops the MutationObserver instance from receiving further notifications until and unless observe() is called again.

observe()

Configures the MutationObserver to begin receiving notifications through its callback function when DOM changes matching the given options occur.

takeRecords()

Removes all pending notifications from the MutationObserver's notification queue and returns them in a new Array of MutationRecord objects.

Example

The following example was adapted from this blog post.

// Select the node that will be observed for mutations
var targetNode = document.getElementById('some-id');

// Options for the observer (which mutations to observe)
var config = { attributes: true, childList: true, subtree: true };

// Callback function to execute when mutations are observed
var callback = function(mutationsList) {
    for(var mutation of mutationsList) {
        if (mutation.type == 'childList') {
            console.log('A child node has been added or removed.');
        }
        else if (mutation.type == 'attributes') {
            console.log('The ' + mutation.attributeName + ' attribute was modified.');
        }
    }
};

// Create an observer instance linked to the callback function
var observer = new MutationObserver(callback);

// Start observing the target node for configured mutations
observer.observe(targetNode, config);

// Later, you can stop observing
observer.disconnect();

See also

• A brief overview
• A more in-depth discussion
• A screencast by Chromium developer Rafael Weinstein
• The mutation summary library

Specifications

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

[1] Prior to Firefox 61, the MutationObserverInit dictionary had a default value of false for all of its Boolean properties. Now only childList and subtree default to false; all other properties have no default value.