promises

[jamiebuilds]

This re-implements parts of setState so that it returns a promise It simplifies a lot about the implementation. The only problem is that we always pass a callback to React's setState which may be a perf issue for some apps.

[jamiebuilds]

cc @sindresorhus

[paul-phan]

Yes, I already facing some problem while using container.setState with controlled component and the setState callback not working sometimes. Seem like this implement will fix the callback issue.

[xat]

If something inside the callback function throws then the error might get swallowed.

[xat]

why not just return this.setState(DUMMY_STATE); (instead of creating a new promise)?

[jamiebuilds]

because then we dont wait for the callback

[sindresorhus]

@jamiebuilds I tried this in our app and it works perfectly.

[ehaynes99]

Why not pick one or the other? There is no need for 2 different mechanisms to notify on update, and the promise version is cleaner and easier to test.

const callback = () => console.log('state updated')

// with callback
setState({
  some: 'newValue',
}, callback)

// with promise
setState({
  some: 'newValue',
}).then(callback)

// sooner or later, someone will do this
const promise = setState({
  some: 'newValue',
}, callback)
promise.then(callback)

[ldthorne]

@jamiebuilds Is there any update on this? I'd love to see this PR merged in -- it makes the setState API consistent with React's API. As others have pointed out, Promises are a much cleaner interface and personally, I'm hesitant to introduce (essentially mandatory) callbacks to my codebase.

[ehaynes99]

@ldthorne This isn't consistent, which is fine, but is different from the behavior of React. React's API does not return a promise, it uses the callback style.

React's API:

• returns undefined
• runs asynchronously
• batches together multiple updates (i.e. multiple setState calls together will only rerender once)
• allows an optional callback

Unstated since version 2:

• returns undefined
• runs asynchronously
• rerenders for every setState call
• allows an optional callback (but they're broken. See Possible fix for broken callbacks #35)

This PR:

• returns a promise that resolves to undefined
• runs asynchronously
• rerenders for every setState call
• allows an optional callback

[ldthorne]

@jamiebuilds can you create a new release for this on NPM? We'd love to start using this in production

[nfort]

@jamiebuilds
Demo problem: https://codesandbox.io/s/0qlkn033v

What about this case?

[jamiebuilds]

@nfort fixed in 2.1.1