reactjs: Does setState() immediately change this.state?

Question

I've experimented some cases in which calling this.setState({ foo: true }) and immediately checking this.state.foo does not return the new value true.

I can't tell now the exact case in which this happens (maybe when calling multiple times to setState() in the same iteration, I don't know). So I wonder:

Does reactjs guarantee that the following will always work?

this.setState({ foo: true });

console.log(this.state.foo);
// => prints true

this.setState is an asynchronous operation, so there are no guarantees. They do state this in the official docs. — ctrlplusb
– ctrlplusb, Commented Sep 13, 2016 at 10:03

Oleksandr T. · Accepted Answer · 2016-09-13 10:04:20Z

5

Does reactjs guarantee that the following will always work?

No, setState is asynchronous method., if you want to get updated state you should use callback as second argument

this.setState({ foo: true }, () => {
  console.log(this.state.foo);
});

answered Sep 13, 2016 at 10:04

Oleksandr T.

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user5738822 · Accepted Answer · 2016-09-13 10:14:23Z

0

It's done asynchronously. So you may not see the update within the method. Check that in componentDidUpdate. or you can see the result in the setState callback , like this :

this.setState({name: nextProps.site.name} , ()=>{

console.log(this.state.name);

});

answered Sep 13, 2016 at 10:14

user5738822

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