React 0.13类方法未定义

Question

So i've started with React and ES6 and got stuck with very basics. Really appreciate some help.

handleClick() throws an error:

Uncaught TypeError: Cannot read property 'handleClick' of undefined

code follows

export default class MenuItems extends React.Component {

  constructor(props) {
    super(props)
    this.state = {active: false}
    this.handleClick = this.handleClick.bind(this)
  }

  handleClick() {
    this.setState({ active: !this.state.active });
  }

  render() {
    let active = this.state.active
    let menuItems = [{text: 'Logo'}, {text:  'promo'}, {text:     'benefits'}, { text: 'form'}]
    return (
      <ul>
        {menuItems.map(function(item) {
          return <li className={active ? 'active' : ''} onClick={this.handleClick.bind(this)} key={item.id}>{item.text}</li>;
        })}
      </ul>
    );
  }
}

Answer 1

{menuItems.map(function(item) {
  return <li className={active ? 'active' : ''} onClick={this.handleClick.bind(this)} key={item.id}>{item.text}</li>;
})}

Because your code is in strict mode (modules are always in strict mode), this is undefined inside the function you pass to .map .

You either have to explicitly set the context by passing a second argument to .map :

{menuItems.map(function(item) {
  // ...
}, this)}

Or use an arrow function :

{menuItems.map(
     item => <li className={active ? 'active' : ''} onClick={this.handleClick.bind(this)} key={item.id}>{item.text}</li>
)}

Answer 2

react.js:18794 Warning: bind(): You are binding a component method to the component. React does this for you automatically in a high-performance way, so you can safely remove this call. See BlueBall

so just like this:

{
  menuItems.map(
     item => <li className={active ? 'active' : ''} 
  onClick={this.handleClick} key={item.id}>{item.text}</li>
)}