reference: https://github.com/vuejs/rfcs/issues/121
BREAKING CHANGE: object returned from `setup()` are no longer implicitly
passed to `reactive()`.
The renderContext is the object returned by `setup()` (or a new object
if no setup() is present). Before this change, it was implicitly passed
to `reactive()` for ref unwrapping. But this has the side effect of
unnecessary deep reactive conversion on properties that should not be
made reactive (e.g. computed return values and injected non-reactive
objects), and can lead to performance issues.
This change removes the `reactive()` call and instead performs a
shallow ref unwrapping at the render proxy level. The breaking part is
when the user returns an object with a plain property from `setup()`,
e.g. `return { count: 0 }`, this property will no longer trigger
updates when mutated by a in-template event handler. Instead, explicit
refs are required.
This also means that any objects not explicitly made reactive in
`setup()` will remain non-reactive. This can be desirable when
exposing heavy external stateful objects on `this`.
BREAKING CHANGE: `createApp` API has been adjusted.
- `createApp()` now accepts the root component, and optionally a props
object to pass to the root component.
- `app.mount()` now accepts a single argument (the root container)
- `app.unmount()` no longer requires arguments.
New behavior looks like the following:
``` js
const app = createApp(RootComponent)
app.mount('#app')
app.unmount()
```
This avoids trying to grab .el from hoisted child nodes (which can
be created by another instance), and also skips transition check
since fragment children cannot have transitions.
Store the keys for props that need default or boolean casting
during normalization, so that later we only need to iterate
through this array instead of the entire props object.
