https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/no-render-return-value.md

ReactDOM.render() currently returns a reference to the root ReactComponent instance. However, using this return value is legacy and should be avoided because future versions of React may render components asynchronously in some cases. If you need a reference to the root ReactComponent instance, the preferred solution is to attach a callback ref to the root element.

Source: ReactDOM documentation

Rule Details

This rule will warn you if you try to use the ReactDOM.render() return value.

Examples of incorrect code for this rule:

const inst = ReactDOM.render(<App />, document.body);
doSomethingWithInst(inst);

Examples of correct code for this rule:

ReactDOM.render(<App ref={doSomethingWithInst} />, document.body);

ReactDOM.render(<App />, document.body, doSomethingWithInst);