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clarify onMount return functions when combined with non-synchronous handlers #5053

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merged 4 commits into from
Jun 23, 2020
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clarify onMount return functions when combined with non-synchronous handlers #5053

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83084f9
clarify onMount with async
antony Jun 23, 2020
3d3663a
make more concise
antony Jun 23, 2020
5b38f7a
modify wording for clarity
antony Jun 23, 2020
2e297ef
make formatting of synchronously consistent
antony Jun 23, 2020
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2 changes: 2 additions & 0 deletions site/content/docs/03-run-time.md
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Expand Up @@ -50,6 +50,8 @@ If a function is returned from `onMount`, it will be called when the component i
</script>
```

> This behaviour will only work when the function passed to `onMount` *synchronously* returns a value. `async` functions always return a `Promise`, and as such cannot *synchronously* return a function.
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Do we want to maybe say "returns a function" rather than "returns a value"? The only thing I'd worry with about that is the ends of the two sentences sounding a bit repetitive.

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@antony antony Jun 23, 2020 •
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The reason I've said value in the first instance, is that I wouldn't consider this:

const myOnDestroy = function () { disposeStuff() } 
onMount(async () => new Promise(r => r(myOnDestroy))

as returning a function, more returning a value. I'd want to cover people literally using promises as return values within async functions.

The second sentence refers to a concrete example.

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That's fair. This seems like a good explanation then, and there'll at least be some place in the docs to point people to about this now.


#### `beforeUpdate`

```js
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