Type of the Children props

Usually, a component’s children (this.props.children) is an array of components:

  1. var GenericWrapper = React.createClass({
  2.   componentDidMount: function() {
  3.     console.log(Array.isArray(this.props.children)); // => true
  4.   },
  6.   render: function() {
  7.     return <div />;
  8.   }
  9. });
  11. ReactDOM.render(
  12.   <GenericWrapper><span/><span/><span/></GenericWrapper>,
  13.   mountNode
  14. );

However, when there is only a single child, this.props.children will be the single child component itself without the array wrapper. This saves an array allocation.

  1. var GenericWrapper = React.createClass({
  2.   componentDidMount: function() {
  3.     console.log(Array.isArray(this.props.children)); // => false
  5.     // warning: yields 5 for length of the string 'hello', not 1 for the
  6.     // length of the non-existent array wrapper!
  7.     console.log(this.props.children.length);
  8.   },
  10.   render: function() {
  11.     return <div />;
  12.   }
  13. });
  15. ReactDOM.render(<GenericWrapper>hello</GenericWrapper>, mountNode);

To make this.props.children easy to deal with, we’ve provided the React.Children utilities.