Can't call setState (or forceUpdate) on an unmounted component : <p>I'm trying to fetch the data from the server after component has been updated but I couldn't manage to do that. As far as I understand <code>componentWillUnmount</code> is called when component is about to be destroyed, but I never need to destroy it so it's useless to me. What would be solution for this? When I should set the state?</p>

<pre><code>async componentDidUpdate(prevProps, prevState) {
  if (this.props.subject.length &amp;&amp; prevProps.subject !== this.props.subject) {
    let result = await this.getGrades({
      student: this.props.id,
      subject: this.props.subject
    });
    this.setState({
      subject: this.props.subject,
      grades: result
    });
  }
}

async getGrades(params) {
  let response, body;

  if (params['subject'].length) {
    response = await fetch(apiRequestString.gradesBySubject(params));
    body = await response.json();
  } else {
    response = await fetch(apiRequestString.grades(params));
    body = await response.json();
  }

  if (response.status !== 200) throw Error(body.message);

  return body;
}
</code></pre>

<p>Full error:</p>

<pre><code>Warning: Can't call setState (or forceUpdate) on an unmounted component. This is a no-op, 
but it indicates a memory leak in your application. To fix, cancel all subscriptions and
asynchronous tasks in the componentWillUnmount method.
</code></pre>
