reactjs - this.setState() not working properly - react.js

Question

componentWillMount() {
        let dID=this.props.match.params.datumID;
        this.setState({datumID: dID});
        console.log(dID);
        console.log(this.state.datumID);
    }

I'm just trying use setState() method.

But the problem is it is not working.

Here is what I get as output:

First console.log() : 66
Second console.log(): null

Answer 1

Think of setState() as a request rather than an immediate command to update the component. For better perceived performance, React may delay it, and then update several components in a single pass. React does not guarantee that the state changes are applied immediately.

If you need to set the state based on the previous state, read about the updater argument below.

    this.setState((prevState, props) => {
       return {datumID: props.match.params.datumID};
    });