Mutation Events, including `DOMSubtreeModified`, `DOMNodeInserted`, `DOMNodeRemoved`, `DOMNodeRemovedFromDocument`, `DOMNodeInsertedIntoDocument`, and `DOMCharacterDataModified`, are quite bad for page performance, and also significantly increase the complexity of adding new features to the Web. These APIs were deprecated from the spec (https://w3c.github.io/uievents/#legacy-event-types) in 2011, and were replaced (in 2012) by the much better-behaved Mutation Observer API. Usage of the obsolete Mutation Events must now be migrated to Mutation Observer. Mutation event support will be disabled by default starting in Chrome 127, around July 30, 2024. Code should be migrated before that date to avoid site breakage. If more time is needed, there are a few options: - The Mutation Events Deprecation trial (https://developer.chrome.com/origintrials/#/view_trial/919297273937002497) can be used to re-enable the feature for a limited time on a given site. This can be used through Chrome 134, ending March 25, 2025. - A MutationEventsEnabled enterprise policy (https://chromeenterprise.google/policies/#MutationEventsEnabled) can also be used for the same purpose, also through Chrome 134. Please see this blog post for more detail: https://developer.chrome.com/blog/mutation-events-deprecation Report bugs here: https://issues.chromium.org/new?component=1456718&template=1948649
Mutation Events have been deprecated for over a decade, with the replacement (Mutation Observer) available also for over a decade. The fact that these events are still supported in browsers makes the addition of new features much more difficult, prohibitively so in some cases. For example, these feature requests and projects are all negatively impacted by the existence of Mutation Events: - iFrame reparenting: https://github.com/whatwg/html/issues/5484 and https://github.com/whatwg/dom/issues/891 - Child reordering: https://github.com/whatwg/dom/issues/586 - DOM Parts and batch DOM updates: https://github.com/WICG/webcomponents/blob/gh-pages/proposals/DOM-Parts.md Given that the feature has been spec-deprecated for over a decade, and a replacement available for over a decade, it makes sense to finally disable and remove these APIs from Chrome.