ReactJS and React Router

• ReactJS is a JavaScript library for building user interfaces
• It allows developers to create reusable UI components
• React uses a component-based architecture
• It employs a virtual DOM to optimize updates to the actual DOM
• React follows a declarative programming style

Routing with React Router

• React Router is a standard library for routing in React applications
• It enables navigation between different views or components
• React Router provides <BrowserRouter>, <Route>, <Switch>, and <Link> components
• <BrowserRouter> uses HTML5 history API for client-side routing
• <Route> renders a UI component when its path matches the current URL
• <Switch> renders the first <Route> that matches the URL exclusively
• <Link> is used for creating navigation links within the application
• Route parameters can be defined using the :paramName syntax
• The useParams hook can access route parameters in functional components
• Nested routes can be created for complex application structures
• Programmatic navigation can be achieved using useHistory hook to access the history instance

Hooks

• Hooks are functions that let you "hook into" React state and lifecycle features from functional components
• useState hook allows functional components to have state variables
• useEffect hook performs side effects in functional components
• useContext hook consumes values from a React context
• useReducer hook manages complex state logic using reducers
• useCallback hook memoizes functions to prevent unnecessary re-renders
• useMemo hook memoizes the result of a computation
• Custom hooks can be created to reuse stateful logic
• Hooks must be called in the same order each time a component renders to preserve state

Component Lifecycle

• Component lifecycle refers to the series of events that occur from the birth to the death of a component instance
• Lifecycle methods are primarily used in class components
• Mounting phase includes constructor, render, and componentDidMount
• Updating phase includes render, componentDidUpdate, and shouldComponentUpdate
• Unmounting phase includes componentWillUnmount
• constructor initializes the component's state and binds event handlers
• render describes the UI to be rendered based on the component's state and props
• componentDidMount is invoked immediately after a component is mounted
• componentDidUpdate is invoked immediately after an update occurs
• componentWillUnmount is invoked immediately before a component is unmounted and destroyed
• getDerivedStateFromProps is a static method called before rendering on mount and subsequent updates
• shouldComponentUpdate determines if a component should re-render, optimizing performance

Performance Optimization

• Identify and address performance bottlenecks
• Use React Developer Tools profiler to identify slow components
• Minimize unnecessary re-renders using React.memo for functional components
• Use shouldComponentUpdate or PureComponent for class components
• Use keys for uniquely identifying list items to help React identify changes
• Lazy load components using React.lazy and Suspense to reduce initial load time
• Code splitting divides application code into smaller chunks improving load times
• Optimize images by compressing them
• Avoid inline function definitions in render methods
• Debounce or throttle event handlers to limit function execution rate
• Virtualize large lists to render only visible items (windowing)

State Management

• State management deals with handling and controlling data throughout an application
• Local state can be managed using useState hook or class component's this.state
• Context API provides a way to pass data through the component tree without manually passing props at every level
• Redux is a predictable state container for managing application state
• Redux uses a single store to hold the entire application state
• Redux reducers specify how the state changes in response to actions
• Redux actions are plain JavaScript objects that describe an event that occurred
• Redux middleware provides a way to intercept and handle actions before they reach the reducer
• Redux Toolkit simplifies common Redux tasks
• MobX is a state management library that uses reactive programming
• Zustand is a small, fast and scalable bearbones state-management solution
• Jotai is a primitive and flexible state management library with an atomic model