Incrementing state value by one using React

Question

In React I am trying to make a button increment a value stored in state. However using the code below function my value is set undefined or NaN when using handleClick.

Answer 1

This is the shortest code for that. First, initialize the state, then perform a method to increment.

state = {
    counter: 0
  }

increaseHandler = () => {
    let counter = this.state.counter
    counter += 1
    this.setState({counter: counter})
  }