Why does React throw an error when using the setState method in the class constructor?

Question

I know that when setting the state for a component that is not yet mounted, an error occurs. This explains the error I get from using the setState function, both against explicitly and directly setting the state.

import React, {Component} from 'react';

class SearchBar extends Component {

constructor(props) {
  super(props);

  this.state = {term: ''}; // -> seems to be the agreed means to set   initial state
// this.setState({term: ''}); // -> generates an error
}

render() {
  return (
    <div>
      <input onChange={event => this.setState({term:   event.target.value})}/>
      Value of the input: {this.state.term}
  </div>
);
  }
}

The error I get when I uncomment the second line of this.setState ({term: ''}):

Warning: setState (...): Can only upgrade mounted or mounted components. This usually means that you called setState () on an unmounted component. This is a no-op. Check the component code.

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Answer 1

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