MutationObserver

MutationObserver provides developers a way to react to changes in a DOM. It is designed as a replacement for Mutation Events defined in the DOM3 Events specification.

Constructor

MutationObserver()

Constructor for instantiating new DOM mutation observers.

new MutationObserver(
  function callback
);

Parameters

callback

The function which will be called on each DOM mutation. The observer will call this function with two arguments. The first is an array of objects, each of type MutationRecord. The second is this MutationObserver instance.

Instance methods

observe()

Registers the MutationObserver instance to receive notifications of DOM mutations on the specified node.

void observe(
  Node target,
  MutationObserverInit options
);

Parameters

target

The Node on which to observe DOM mutations.

options

A MutationObserverInit object, specifies which DOM mutations should be reported.

disconnect()

Stops the MutationObserver instance from receiving notifications of DOM mutations. Until the observe() method is used again, observer's callback will not be invoked.

void disconnect();

takeRecords()

Empties the MutationObserver instance's record queue and returns what was in there.

Array takeRecords();

Return value

Returns an Array of MutationRecords.

MutationObserverInit

MutationObserverInit is an object which can specify the following properties:

Example usage

The following example was taken from this blog post.

// select the target node
var target = document.getElementById('some-id');
 
// create an observer instance
var observer = new MutationObserver(function(mutations) {
  mutations.forEach(function(mutation) {
    console.log(mutation.type);
  });    
});
 
// configuration of the observer:
var config = { attributes: true, childList: true, characterData: true };
 
// pass in the target node, as well as the observer options
observer.observe(target, config);
 
// later, you can stop observing
observer.disconnect();

Additional reading

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

Specifications

Browser compatibility