Improve handling of undo/redo events in web demo (#1254)

[garyg1]

Fixes #1254. In the demo on https://jsonnet.org, if you hit redo/undo for multiple characters, the demo breaks. This seems to be because the browser generates multiple text change events (Chrome 139, MacOS 14.6).

Previous Behavior

https://jsonnet.org/

Screen.Recording.2025-09-02.at.8.12.12.PM.mov

New Behavior

Screen.Recording.2025-09-02.at.8.12.43.PM.mov

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[johnbartholomew]

So if I understand correctly you're using this to serialise processing each of the change events?

I think that's ok. Though I think there's another way to do it without the setTimeout: You can keep a reference to an 'ongoing change' to await, and then chain them. Something like this:

    let ongoingChange = Promise.resolve(true);
    editor.on('change', function() {
        return ongoingChange.then(async () => {
            try {
                // previous change is complete and future changes are queued on our promise
                // do the event processing
            } catch (e) {
                // log the error; if it unwinds further then it'll break the Promise chain
            }
        });
    });

What do you think? (I haven't tried running this to verify it!)

[johnbartholomew]

Thanks for the contribution! It's great to have a fix for this!