react.dev/docs/advanced-components.md

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docs-advanced-components	Advanced Components	How to build advanced composite components.	docs	event-handling.html	api.html

Composite components extend a ReactCompositeComponent base class that provides a very powerful API that makes React flexible and able to easily work with other libraries and frameworks.

Lifecycle Methods

Composite components can optionally implement lifecycle methods that are invoked at various stages in the component lifecycle that each have unique guarantees.

Mounting

• getInitialState(): object is invoked before a component is mounted. Stateful components should implement this and return the initial state data.
• componentWillMount() is invoked immediately before mounting occurs.
• componentDidMount(DOMElement rootNode) is invoked immediately after mounting occurs. Initialization that requires DOM nodes should go here.

Updating

• componentWillReceiveProps(object nextProps) is invoked when a mounted component receives new props. This method should be used to compare this.props and nextProps to perform state transitions using this.setState().
• shouldComponentUpdate(object nextProps, object nextState): boolean is invoked when a component decides whether any changes warrant an update to the DOM. Implement this as an optimization to compare this.props with nextProps and this.state with nextState and return false if React should skip updating.
• componentWillUpdate(object nextProps, object nextState) is invoked immediately before updating occurs. You cannot call this.setState() here.
• componentDidUpdate(object prevProps, object prevState, DOMElement rootNode) is invoked immediately after updating occurs.

Unmounting

• componentWillUnmount() is invoked immediately before a component is unmounted and destroyed. Cleanup should go here.

Mounted Methods

Mounted composite components also support the following methods:

• getDOMNode(): DOMElement can be invoked on any mounted component in order to obtain a reference to its rendered DOM node.
• forceUpdate() can be invoked on any mounted component when you know that some deeper aspect of the component's state has changed without using this.setState().

Note:

The DOMElement rootNode argument of componentDidMount() and componentDidUpdate() is a convenience. The same node can be obtained by calling this.getDOMNode().

Component Refs

A common use case of event callbacks or the lifecycle methods is to operate on a component returned by render(). For example, consider a search component that should auto-focus the input once mounted:

var SearchForm = React.createClass({
  render: function() {
    return (
      <form action={this.props.action}>
        <input type="search" placeholder="Search..." />
      </form>
    );
  },
  componentDidMount: function(rootNode) {
    var searchInput = rootNode.firstChild;
    searchInput.focus();
  }
});

Although this implementation works, it is fragile because componentDidMount() now relies on render() returning a particular DOM structure.

React provides a better way for composite components to reference components that it constructs in its render() method through the use of refs. A component can assign a ref to any component it constructs. This will create a reference to those components on this.refs. For example:

var SearchForm = React.createClass({
  render: function() {
    return (
      <form action={this.props.action}>
        <input type="search" placeholder="Search..." ref="searchInput" />
      </form>
    );
  },
  componentDidMount: function(rootNode) {
    var searchInput = this.refs.searchInput.getDOMNode();
    searchInput.focus();
  }
});

In this example, this.refs.searchInput will reference the <input> component and is available in most lifecycle methods and event callbacks. We obtain a reference to the <input>'s DOM node using getDOMNode().

Note:

If you want to preserve compatibility with Google Closure Compiler's property crushing in ADVANCED_OPTIMIZATIONS mode, make sure to use string literals with this.refs.