Is MutationRecord.oldValue something I should be using?

Question

I'm using the latest Google Chrome stable (19.0.1084.56 m) on Windows 7 and experimenting with Mutation observers for the first time. (The project is a user script for a third party website, the server of which I have no access to.)

So it happens that MutationRecord has a field oldValue:

record . oldValue

The return value depends on type. For "attributes", it is the value of the changed attribute before the change. For "characterData", it is the data of the changed node before the change. For "childList", it is null.

So I'm monitoring for changes to the characterData but when I get the MutationRecord the oldValue field is always null.

Should it be working, is there a possibility I've got something wrong, or is this feature just too bleeding edge to expect to work yet?

Is there somewhere I can find Google's documentation, bug report, feature request, etc that might declare whether this is implemented or when it might be?

Answer 1

Configure your observer with:

observer.observe(container, {
    attributeOldValue : true
});

Full API documentation: https://developer.mozilla.org/pt-BR/docs/Web/API/MutationObserver