react.dev/tips/16-references-to-components.md

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references-to-components	References to Components	tips	references-to-components.html	expose-component-functions.html

If you're using React components in a larger non-React application or transitioning your code to React, you may need to keep references to components. React.renderComponent returns a reference to the mounted component:

/** @jsx React.DOM */

var myComponent = React.renderComponent(<MyComponent />, myContainer);

If you pass a variable to 'React.renderComponent`, it's not guaranteed that the component passed in will be the one that's mounted. In cases where you construct a component before mounting it, be sure to reassign your variable:

/** @jsx React.DOM */

var myComponent = <MyComponent />;

// Some code here...

myComponent = React.renderComponent(myComponent, myContainer);

Note:

This should only ever be used at the top level. Inside components, let your props and state handle communication with child components, and only reference components via refs.