React is a JavaScript library for creating user interfaces that is fast and flexible (and React itself is written using JavaScript). Complex user interfaces are broken down into "components," which are small, separate pieces of code. React only cares about what you see on a website's front page when you use these components or we can say ReactJS is a JavaScript library for creating reusable user interface components that is declarative, efficient, and versatile. It's a component-based front end library that's only responsible for the application's view layer.
A ReactJS application consists of several components, each of which is responsible for producing a short, reusable piece of HTML code. All React apps are built around components. These components can be stacked with one other to create sophisticated applications from simple building blocks. To populate data in the HTML DOM, ReactJS uses a virtual DOM-based technique. The virtual DOM is quick because it simply modifies individual DOM elements rather than reloading the entire DOM every time.
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