React: “this” is undefined inside a component function

Question

class PlayerControls extends React.Component {
  constructor(props) {
    super(props)

    this.state = {
      loopActive: false,
      shuffleActive: false,
    }         


        

Answer 1

Write your function this way:

onToggleLoop = (event) => {
    this.setState({loopActive: !this.state.loopActive})
    this.props.onToggleLoop()
}

Fat Arrow Functions

the binding for the keyword this is the same outside and inside the fat arrow function. This is different than functions declared with function, which can bind this to another object upon invocation. Maintaining the this binding is very convenient for operations like mapping: this.items.map(x => this.doSomethingWith(x)).