MutationObserver

{{APIRef("DOM WHATWG")}} 

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

• {{domxref("MutationObserver.MutationObserver", "MutationObserver()")}} 
  • : Creates and returns a new MutationObserver which will invoke a specified callback function when DOM changes occur.

Instance methods

• {{domxref("MutationObserver.disconnect()", "disconnect()")}} 
  • : Stops the MutationObserver instance from receiving further notifications until and unless {{domxref("MutationObserver.observe", "observe()")}}  is called again.
• {{domxref("MutationObserver.observe()", "observe()")}} 
  • : Configures the MutationObserver to begin receiving notifications through its callback function when DOM changes matching the given options occur.
• {{domxref("MutationObserver.takeRecords()", "takeRecords()")}} 
  • : Removes all pending notifications from the MutationObserver’s notification queue and returns them in a new {{jsxref("Array")}}  of {{domxref("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 = (mutationList, observer) => {
  for (const mutation of mutationList) {
    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

{{Specifications}} 

Browser compatibility

{{Compat}} 

See also

• {{domxref('PerformanceObserver')}} 
• {{domxref('ResizeObserver')}} 
• {{domxref('IntersectionObserver')}} 
• A brief overview
• A more in-depth discussion
• A screencast by Chromium developer Rafael Weinstein