What is the difference between using constructor vs state = {} in React / React Native? [duplicate]

Question

I have seen both

export default class LoginScreen extends React.Component {
  constructor(props){
    super(props);
    this.state = {
      loading: false,
      loggedIn: false,
    }
  }
}

and

export default class LoginScreen extends React.Component {
  state = {
    loading: false,
    loggedIn: false,
  }
}

What are the use cases for both? Are there advantages / disadvantages? Is one a better practice?

Answer 1

Use constructor when you want to save props data into state

export default class LoginScreen extends React.Component {
  constructor(props){
    super(props);
    this.state = {
      loading: props.loading,
      loggedIn: props.loggedIn,
    }
  }
}

Otherwise you can directly set the state for hard coded data

export default class LoginScreen extends React.Component {
  state = {
    loading: false,
    loggedIn: false,
  }
}