Identify new / changed data from pub/sub on client

help
1

Hi,

Is there an easy way to identify the new / changed data from pub/sub on the client?

I am using Grapher withQuery.

My initial plan was to track the previous pub/sub state using a custom usePrevious React hook and check for differences, but I wondered if there was a Meteor/Grapher way to do this already?

Thanks,
Alex

2

If I understand you correctly, you want to tap into the event when pub/sub data gets changed, and you also want to have the pubsub state before the change. A react class component’s componentDidUpdate(prevProps) might give you just that.

But that’s conspicuously easy, so you probably have meant something else :slight_smile:

3

Hi @peterfkruger,

Yes, pretty much. I need to do something different depending on what is different with the newly published data.

For example, if a new document has been added, I want to do X. If the change was caused by an existing document changing, then I don’t want to do anything.

I was just wondering if Meteor or Grapher had some built-in functionality to check this.

I guess not - I’ll go with the prevProps method instead.

4

You should check out Cursor.observe (and observeChanges).

You’d probably want to set that up in useEffect instead of using useTracker if you use those.

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