[javascript] React setState not updating state

So I have this:

let total = newDealersDeckTotal.reduce(function(a, b) {
  return a + b;
},
0);

console.log(total, 'tittal'); //outputs correct total
setTimeout(() => {
  this.setState({dealersOverallTotal: total});
}, 10);

console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); //outputs incorrect total

newDealersDeckTotal is just an array of numbers [1, 5, 9] e.g. however this.state.dealersOverallTotal does not give the correct total but total does? I even put in a timeout delay to see if this solved the problem. any obvious or should I post more code?

I had the same situation with some convoluted code, and nothing from the existing suggestions worked for me.

My problem was that setState was happening from callback func, issued by one of the components. And my suspicious is that the call was occurring synchronously, which prevented setState from setting state at all.

Simply put I have something like this:

render() {
    <Control
        ref={_ => this.control = _}
        onChange={this.handleChange}
        onUpdated={this.handleUpdate} />
}

handleChange() {
    this.control.doUpdate();
}

handleUpdate() {
    this.setState({...});
}

The way I had to "fix" it was to put doUpdate() into setTimeout like this:

handleChange() {
    setTimeout(() => { this.control.doUpdate(); }, 10);
}

Not ideal, but otherwise it would be a significant refactoring.

setState is asynchronous. You can use callback method to get updated state.

changeHandler(event) {
    this.setState({ yourName: event.target.value }, () => 
    console.log(this.state.yourName));
 }

I had an issue when setting react state multiple times (it always used default state). Following this react/github issue worked for me

const [state, setState] = useState({
  foo: "abc",
  bar: 123
});

// Do this!
setState(prevState => {
  return {
    ...prevState,
    foo: "def"
  };
});
setState(prevState => {
  return {
    ...prevState,
    bar: 456
  };
});

The setState() operation is asynchronous and hence your console.log() will be executed before the setState() mutates the values and hence you see the result.

To solve it, log the value in the callback function of setState(), like:

setTimeout(() => {
    this.setState({dealersOverallTotal: total},
    function(){
       console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
    });
}, 10)

In case of hooks, you should use useEffect hook.

const [fruit, setFruit] = useState('');

setFruit('Apple');

useEffect(() => {
  console.log('Fruit', fruit);
}, [fruit])

Using async/await

async changeHandler(event) {
    await this.setState({ yourName: event.target.value });
    console.log(this.state.yourName);
}

just add componentDidUpdate(){} method in your code, and it will work. you can check the life cycle of react native here:

https://images.app.goo.gl/BVRAi4ea2P4LchqJ8

The setstate is asynchronous in react, so to see the updated state in console use the callback as shown below (Callback function will execute after the setstate update)

The below method is "not recommended" but for understanding, if you mutate state directly you can see the updated state in the next line. I repeat this is "not recommended"

As well as noting the asynchronous nature of setState, be aware that you may have competing event handlers, one doing the state change you want and the other immediately undoing it again. For example onClick on a component whose parent also handles the onClick. Check by adding trace. Prevent this by using e.stopPropagation.