freeCodeCamp/curriculum/challenges/english/03-front-end-libraries/react/use-the-lifecycle-method-componentwillmount.english.md

id, title, challengeType, isRequired

id	title	challengeType	isRequired
5a24c314108439a4d403617c	Use the Lifecycle Method componentWillMount	6	false

Description

React components have several special methods that provide opportunities to perform actions at specific points in the lifecycle of a component. These are called lifecycle methods, or lifecycle hooks, and allow you to catch components at certain points in time. This can be before they are rendered, before they update, before they receive props, before they unmount, and so on. Here is a list of some of the main lifecycle methods: componentWillMount() componentDidMount() componentWillReceiveProps() shouldComponentUpdate() componentWillUpdate() componentDidUpdate() componentWillUnmount() The next several lessons will cover some of the basic use cases for these lifecycle methods.

Note: The componentWillMount Lifecycle method will be deprecated in a future version of 16.X and removed in version 17. (Source)

Instructions

The componentWillMount() method is called before the render() method when a component is being mounted to the DOM. Log something to the console within componentWillMount() - you may want to have your browser console open to see the output.

Tests

tests:
  - text: <code>MyComponent</code> should render a <code>div</code> element.
    testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); return mockedComponent.find('div').length === 1; })(), '<code>MyComponent</code> should render a <code>div</code> element.');
  - text: <code>console.log</code> should be called in <code>componentWillMount</code>.
    testString: assert((function() { const lifecycle = React.createElement(MyComponent).type.prototype.componentWillMount.toString().replace(/ /g,''); return lifecycle.includes('console.log('); })(), '<code>console.log</code> should be called in <code>componentWillMount</code>.');

Challenge Seed

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
  }
  componentWillMount() {
    // change code below this line

    // change code above this line
  }
  render() {
    return <div />
  }
};

After Test

ReactDOM.render(<MyComponent />, document.getElementById('root'))

Solution

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
  }
  componentWillMount() {
    // change code below this line
    console.log('Component is mounting...');
    // change code above this line
  }
  render() {
    return <div />
  }
};