Is it good to use `setState()` in `componentWillMount()` method?

Yes, it is safe to use setState() inside componentWillMount() method. But at the same it is recommended to avoid async initialization in componentWillMount() lifecycle method. componentWillMount() is invoked immediately before mounting occurs. It is called before render(), therefore setting state in this method will not trigger a re-render. Avoid introducing any side-effects or subscriptions in this method. We need to make sure async calls for component initialization happened in componentDidMount() instead of componentWillMount().

componentDidMount() {
axios.get(`api/todos`)
  .then((result) => {
    this.setState({
      messages: [...result.data]
    })
  })
}