React setState not updating state

Question

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?

Answer 1

setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:

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

Answer 2

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));
 }

Answer 3

setState() takes time to mutate the value and you javascript 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)

Answer 4

Using async/await

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