StrictMode highlighting problems in an application.

IMP: Strict mode checks are run in development mode only;

IMP: they do not impact the production build.

import ReactDOM, { findDOMNode } from 'react-dom';
import React, { Component, StrictMode } from 'react';

class App extends Component {
	constructor() {
		this.state = { count: 0 };

	componentDidMount() {
		const node = findDOMNode(this);

		// Set red color to our <h1> tag. = 'red';

	render() {
		return (

export default App;

he `findDOMNode()` method is DEPREACTED for that we get the Warning with `<StrictMode>`

In above example we can see the error:

Warning: findDOMNode is deprecated in StrictMode. findDOMNode was passed an instance of App which is inside StrictMode. Instead, add a ref directly to the element you want to reference. Learn more about using refs safely here:

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