MutationObserver: takeRecords() method

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This feature is well established and works across many devices and browser versions. Its been available across browsers since July 2015.

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The MutationObserver method takeRecords() returns a list of all matching DOM changes that have been detected but not yet processed by the observer's callback function, leaving the mutation queue empty.

The most common use case for this is to immediately fetch all pending mutation records immediately prior to disconnecting the observer, so that any pending mutations can be processed when shutting down the observer.

Syntax

takeRecords()

Parameters

None.

Return value

An array of MutationRecord objects, each describing one change applied to the observed portion of the document's DOM tree.

Note: The queue of mutations which have occurred, but not been delivered to the observer's callback is left empty after calling takeRecords().

Examples

In this example, we demonstrate how to handle any undelivered MutationRecords by calling takeRecords() just before disconnecting the observer.

const targetNode = document.querySelector("#someElement");
const observerOptions = {
  childList: true,
  attributes: true,
};

const observer = new MutationObserver(callback);
observer.observe(targetNode, observerOptions);

/* later, when it's time to stop observing */

/* handle any still-pending mutations */

let mutations = observer.takeRecords();

observer.disconnect();

if (mutations.length > 0) {
  callback(mutations);
}

The code fetches any unprocessed mutation records, then invokes the callback with the records so that they can be processed. This is done immediately prior to calling disconnect() to stop observing the DOM.