React.js is an open-source Javascript library for building user interfaces.
It primarily used for single-page applications where user interactions are dynamic and often require updating parts of the page without a full reload.
React.js Developed and maintained by Meta formally known as Facebook.
It has gained widespread adoption in the web development community due to its simplicity, performance, and flexibility and has become one of the most widely used libraries for building interactive and dynamic web applications.
React follows a component-based architecture, where the UI is broken down into small reusable components that manage their state and lifecycle in its component. This approach promotes code reusability, maintainability, and scalability, making it easier to build and maintain complex UIs.
Supports server-side rendering (SSR) with frameworks like Next.js, improving the initial load performance and SEO of web applications.
React Library is Ideal for building Single Page Applications (SPAs) where a single HTML page is dynamically updated in response to user interactions, without the need for page reloads.
Suitable for building complex and interactive user interfaces with dynamic data rendering, form handling, state management, and more.
Reusable Components: React applications are built using components, which are reusable, self-contained building blocks for UI elements. Components can be either functional components (using functions) or class components (using ES6 classes).
JSX (Javascript Extensions): JSX is a syntax extension for Javascript recommended by React. It allows us to write HTML elements and components in a syntax that looks similar to XML or HTML.
Virtual DOM instead of Real DOM: Virtual DOM optimises batch updates to the actual DOM, improving performance and reducing the number of direct DOM manipulations and it updates only those elements marked Dirty by React while reconciliation processing in the DOM tree.
Unidirectional Data Flow: In React.js data flow is unidirectional, which means we can pass data from parent component to child component not vice-versa.
Optimization: It uses various techniques to achieve optimization in applications such as Lazy loading, Code Splitting, Automatic Batching, useCallback Hook, useMemo Hook, React.memo and many more.
State and Props: React components can have an internal state, which is used to manage data that can change over time. Props (short for properties) are used to pass data from a parent component to a child component.
Lifecycle Methods: Before Hooks was Introduced, we had class components in React that had multiple lifecycle methods that allow developers to hook into different phases of a component's life, such as when it is first mounted, updated, or unmounted. After Hooks was introduced, we now have only one `useEffect` hook method which allows developers to hook into different phases of a component's life.
React Hooks: Hooks were introduced in the 16.8 React version. Hooks are functions that allow developers to use state and lifecycle features in functional components, making them more powerful and eliminating the need for class components in many cases.
Rich Ecosystem: Supported by a vast ecosystem of libraries, tools, and community-contributed packages (e.g., React Router, Redux, Next.js) that extend its capabilities and provide solutions for routing, state management, server-side rendering, and more.