feat: allow computed properties within useMeta

[danielroe]

Usage:
In addition to the existing usage for useMeta, this adds the possibility to pass a function which will effectively generate a computed head state and be merged with any other head values.

useMeta(() => ({ title: message.value }))

nuxt-community/typescript-template#225

closes #254

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[danielroe]

@mathe42 I've reverted much of the special handling of titleTemplate as it seems to work now with an initial null value - but want to check there are no gotchas I'm unaware of. Would value your thoughts.

[mathe42]

When null doesn't overwrite the global meta data it's fine.

I can't test this in the next 2 weeks

[axelhzf]

Is it possible that there is a bug here?

Is it possible that pushing something to computedHead add the computedRef at component level instead of instance level?

I am trying to debug a problem where a meta tag is repeated use the function syntax useMeta(() => ({ ... }))

[danielroe]

Have you added the hid property to deduplicate?

[axelhzf]

You are right, I am not adding the property hid, but I think that the property only will hide the problem.

The problem is not related to several components trying to write the same property. I only have one component on the tree trying using useMeta

 setup() {
    useMeta(() => {
      return {
        meta: [
          { property: 'og:title', content: 'page title' }
        ]
      }
    });
  }

The problem I am facing is that every request is adding a new duplicated property (I am doing server-side rendering). So I think that somehow, the state is being stored between each request.

If I print the value _computedHead here https://github.com/nuxt-community/composition-api/pull/255/files#diff-e0058ab35c645c7435fbc38c50432eabeec5d30d5ad15c4278e083edb897842dR106 I can see that it add a new entry on each request.

I will try to create a minimal reproduction repository.

[axelhzf]

Here is the repository https://github.com/axelhzf/nuxt-use-meta-bug

[danielroe]

Thanks @axelhzf - good catch.