To put it simply, React is a JavaScript library for building composable user interfaces. This means that we can build a user interface by composing items called components. A component is an element that contributes to building a user interface. It could be a textbox, a button, a whole form, a group of other components, and so on. Even the entire application's user interface is a component. So, React encourages the creation of components to build a user interface; it's even better if these components are reusable.

React components have the ability to present data that changes over time, and the visualization of that changing data is automatic when we follow a few guidelines.

Since the library deals with user interfaces, you may wonder which presentational design patterns React was inspired by: Model-View-Controller, Model-View-Presenter, Model-View-ViewModel, or something else. React is not bound to a specific presentational pattern. React implements the View part of the most common patterns, leaving developers free to choose the best approach to implement the model, the presenter, and everything else they need to build their application. This aspect is important, since it allows us to classify it as a library, not as a framework; therefore, comparisons with frameworks such as Angular may throw up some inconsistencies.