The MutationObserverInit dictionary's optional characterDataOldValue property is used to specify whether or not the MutationRecord.oldValue property for DOM mutations should be set to the previous value of text nodes which changed.

If you set the MutationObserverInit.characterData property to true but don't set characterDataOldValue to true as well, the MutationRecord will not include information describing the prior state of the text node's contents.

Character data changes are detectable on any text node, including nodes based on the Text, ProcessingInstruction, and Comment interfaces.


var options = {
  characterDataOldValue: true | false


A Boolean value indicating whether or not to set the MutationRecord's oldValue property to be a string containing the value of the character node's contents prior to the change represented by the mutation record.

By default, only changes to the text of the node specified as the target parameter when you called observe() are monitored. To watch for changes to the text contents of all descendants of target, set the subtree option to true.

If you set characterDataOldValue to true, characterData is automatically assumed to be true, even if you don't expressly set it as such.



DOM Standard (DOM)
# ref-for-dom-mutationobserverinit-characterdataoldvalueā‘ 

Browser compatibility

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