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.

Mutation Observer & customize resize event listener & demo

https://codepen.io/milofultz/pen/LYjPXPw

Example

The following example was adapted from this blog post.

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

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

// Callback function to execute when mutations are observed
const callback = function(mutationsList, observer) {
    // Use traditional 'for loops' for IE 11
    for(const 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
const observer = new MutationObserver(callback);

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

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

Specifications

Specification
DOM Standard # interface-mutationobserver

Browser compatibility

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