CallBack or Not for parameter within this.setState

Can anyone explain the ‘rule of thumb’ for the this.setState parameter in React component (Create a Controlled Input):

handleChange(event) {
  this.setState({
    input: event.target.value
  })
}

When should we do like above, and when should we write as a callback like below:

increment() {
    this.setState((state, props) => {
      return state.count += 1;
    })
  }

Thank you!

Tell us what’s happening:
Describe your issue in detail here.

  **Your code so far**

class ControlledInput extends React.Component {
constructor(props) {
  super(props);
  this.state = {
    input: ''
  };
  // Change code below this line
  this.handleChange = this.handleChange.bind(this);
  // Change code above this line
}
// Change code below this line
handleChange(event) {
  this.setState({
    input: event.target.value
  })
}
// Change code above this line
render() {
  return (
    <div>
      { /* Change code below this line */}
      <input type="text" value={this.state.input} onChange={this.handleChange} />
      { /* Change code above this line */}
      <h4>Controlled Input:</h4>
      <p>{this.state.input}</p>
    </div>
  );
}
};
  **Your browser information:**

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.71 Safari/537.36

Challenge: Create a Controlled Input

Link to the challenge:

It depends if the new state is determined by previous state and props - the first one you showed the state always come from user input for which you don’t need to know previous value of the state, the second one increases a value in the state by 1 each time and for that you need to know previous value

Ooh! If it’s stateful, then we need a callback, if it’s stateless, no need for callback… Thanks!

Careful, a stateless component doesn’t have a state at all

Just as an aside, you do not have access to the event target inside the updater function with the version of React that the curriculum is using.

1 Like

Ooh! Gotcha! Thanks!