Incrementing state value by one using React

set state is async so you wont see the value update when the console.log happens. You should have the state value printed out on the UI so you can see whats happening. To fix the console log try this.

class QuestionList extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: 0};
  }

   handleClick = (prevState) => {
    this.setState({value: prevState.value + 1}, () => {
        console.log(this.state.value)
    });
  }

NOTE: when you define an inline lambda (arrow function) for a react class this is bound correctly so you dont need to bind it in the constructor.

also you can change the way you pass the previous number if its just a state increment like this

handleClick = () => {
    this.setState({value: this.state.value + 1}, () => {
        console.log(this.state.value)
    });
}

Because you are using the handleClick function incorrectly. Here:

handleClick = (prevState) => { .... }

prevState will be an event object passed to handleClick function, you need to use prevState with setState, like this:

handleClick = () => {
    this.setState(prevState => {
       return {count: prevState.count + 1}
    })
}

Another issue is, setState is async so console.log(this.state.value) will not print the updated state value, you need to use callback function with setState.

Check more details about async behaviour of setState and how to check updated value.

Check the working solution:

class App extends React.Component {
 
   constructor(props){
       super(props);
       this.state={ count: 1}
   }
 
  onclick(type){
      this.setState(prevState => {
         return {count: type == 'add' ? prevState.count + 1: prevState.count - 1}
      });
  }

   render() {
    return (
      <div>
        Count: {this.state.count}
        <br/>
        <div style={{marginTop: '100px'}}/>
        <input type='button' onClick={this.onclick.bind(this, 'add')} value='Inc'/>
        <input type='button' onClick={this.onclick.bind(this, 'sub')} value='Dec'/>
       </div>
     )
   }
}

ReactDOM.render(
  <App />,
  document.getElementById('container')
);

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>

<div id='container'></div>