Why the audit is important
The following mutation events harm performance and are deprecated in the DOM events spec:
How to pass the audit
Under URLs, Lighthouse reports each mutation event listener that it found
in your code. Replace each of these mutation events with a
MutationObserver on MDN for more help.
How the audit is implemented
This section explains how this audit is implemented, so that you can understand how the audit's score is calculated.
Lighthouse collects all of the event listeners on the page, and flags any listener that uses one of the types listed in Why the audit is important.