unnecessary constructor in react class

Question

If you need to specify initial state in a class, I see people did this

class App extends React.Component {
   constructor() { super(); this.state = { user: [] } }
   render() {
      return <p>Hi</p>
   }
}

but what's wrong without a constructor?

class App extends React.Component {
   state = { user: [] }
   render() {
      return <p>Hi</p>
   }
}

Felix Kling · Accepted Answer · 2017-12-15 16:34:00Z

11

but what's wrong without a constructor?

There is nothing "wrong" with it. But it uses the class properties proposal which is not officially part of the language yet (since you tagged the question with ecmascript-6: It is not part of ES6). So you have to correctly configure your build system to be able to use it (in addition to what's needed for JSX).

answered Dec 15, 2017 at 16:34

Felix Kling

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3 Comments

Tobias Over a year ago

Just an addition to Felix's answer: If you don't want to use the constructor (I'm not a fan of it) you can also use componentWillMount to set the state with setState(...). Then you don't need the super() call which saves a few lines of code.

Jenny Mok Over a year ago

@Tobias isn't it just simply do state = {myapp:'something'} will do? why need to setState with componentWillMount at all?

Tobias Over a year ago

Well most of the time I‘m not just setting static values, but computed ones. That‘s not possible with class properties. To unify my code I use componentWillMount everywhere

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