Defining store computed property after it is referenced in a template causes initial value to be undefined

[btakita]

It does not seem like store can be used in the repl (sveltejs/v2.svelte.dev#213), so I'll explain the issue here.

I am mixing in computed properties into a store. It does not seem like the initial value of newly created store computed properties bubble up to the template.

<p>{{$name}}</p>

<script>
  export default {
    oncreate() {
      this.store.compute('name', ['user'], user => user && user.name)
      this.store.set({user: {name: 'Joe'}})
    }
  }
</script>

To alleviate this issue, I added a compute wrapper:

export function compute(store, name, deps, fn) {
  const values__deps = []
  for (let i=0; i < deps.length; i++) {
    values__deps.push(store.get(deps[i]))
  }
  const __set = {}
  __set[name] = fn(...values__deps)
  store.set(__set)
  store.compute(name, deps, fn)
  return store
}

[btakita]

With the v2 upgrade, the compute helper function is now:

export function compute(store, name, deps, fn) {
  const values__deps = []
  const state = store.get()
  for (let i=0; i < deps.length; i++) {
    values__deps.push(state[deps[i]])
  }
  const __set = {}
  __set[name] = fn(...values__deps)
  store.set(__set)
  store.compute(name, deps, fn)
  return store
}

[Rich-Harris]

Thanks — it looks like this works in the current version — it's possible that it was fixed since you opened this.

Let me know if I'm closing this issue in error.

[btakita]

It's a matter of the ordering. The issue occurs if you call this.store.set before this.store.compute...

https://svelte.technology/repl?version=2.2.0&gist=a0548b9dafee301e890541a0d1ee4c6a

[Rich-Harris]

Fixed in 2.4.3, thanks