NodeJS is open-source, cross-platform JavaScript runtime environment that run on V8 engine, it allows you to create servers, web apps, command line tools , API's and scripts which can be used for backend application development.

ReactJS is a frontend Javascript framework used for developing web application, DOM manipulation is done for rendering the HTML to the frontend.

So you need both for a complete web application development , NodeJS for Backend to execute the business logic and get the data from the database in the form of API's and ReactJS for Frontend which calls the NodeJS API's and display the data to the frontend using data binding to the HTML.