How to use the increment operator in React

Question

Why when I am doing this.setState({count:this.state.count*2}) it is working, but when I am doing: this.setState({count:this.state.count++}) it is not working?

Why, and how to fix it?

Full code:

var Hello = React.createClass({     getInitialState:function(){     return {count:parseInt(this.props.count)}   },     a:function(){     this.setState({count:this.state.count++})     console.log(this.state)   },   render: function() {     console.log(this.state)     return <div onClick={this.a}>Click to increment the counter<b> {this.state.count} </b></div>;   } });  ReactDOM.render(   <Hello count="1" />,   document.getElementById('container') ); 

But this code is working:

a:function(){     this.setState({count:this.state.count*2})     console.log(this.state)   }, 

JSFiddle: https://jsfiddle.net/69z2wepo/55100/

Answer 1

setState is an async function. React may batch a bunch of setStates together. So the value of this.state.count is the value at the time you make the request.

A better solutions to call a function that gets evaluated at the time the setState gets executed.

this.setState((prevState, props) => ({     counter: prevState.counter + 1 }));  

from https://facebook.github.io/react/docs/state-and-lifecycle.html