MutationEvent: prevValue property
Deprecated
To be removed
This feature is pending removal from browsers. Using it now may lead to broken functionality in future updates. Mutation events negatively impact performance and they were selected for removal from the web as part of Interop 2025.
Use the following features instead: MutationObserver.
Non-standard: This feature is not standardized. We do not recommend using non-standard features in production, as they have limited browser support, and may change or be removed. However, they can be a suitable alternative in specific cases where no standard option exists.
The prevValue read-only property of the MutationEvent interface returns a string. In DOMAttrModified events, it represents the previous value of the Attr node. In DOMCharacterDataModified events, it contains the previous value of the CharacterData node. In all other cases, returns the empty string ("").
Value
A string.
Examples
element.addEventListener("DOMAttrModified", (event) => {
console.log(event.previousValue);
});