Monthly Archives: April 2019

React Component: A pair of componentDidMount() and componentWillUnmount() may cause infinite loop if error is thrown from render

The following will cause an infinite loop. The render() method will be called again and again.

class ToDoItemEditComponentContainer extends React.Component {
    componentDidMount() {        
        this.props.loadItem();  //load item remotely and put it in the local redux store      
    }

    componentWillUnmount() {
        this.props.clearItemLocally(); //remove item from local redux store
    }

    render() {
        throw "some error" 
    }
}

Here is why: "As of React 16, errors that were not caught by any error boundary will result in unmounting of the whole React component tree. " (See here). To be more specific,

  • render() throws an error
  • The react component tree is unmounted
  • componentWillUnmount() is called. And something is cleared from the reduxt store or react state
  • The component tree will be rendered again since some state has been changed

To fix: Implement componentDidCatch() hook in this component or create a global error boundary as shown in here . When there is a render() error, do not call the render() method any more, or do not change any local data in componentWillUnmount()