Introduction to React Hooks
React Hooks are functions that let you use state and other React features in functional components. They were introduced to simplify component logic and eliminate the need for class-based components in most cases.
Why Hooks Were Introduced
Before Hooks, state and lifecycle features were only available in class components. Hooks allow functional components to manage local state, perform side effects, access context, and more, making code easier to write, test, and reuse.
Benefits of Using Hooks
- Promotes reuse of logic across components
- Reduces complexity by avoiding classes
- Makes components more concise and readable
- Enables better separation of concerns in component design
Most Commonly Used Hooks
There are several built-in Hooks that cover a wide range of features. The most commonly used are those for managing state, handling side effects, and referencing DOM elements directly.
Rules of Hooks
- Hooks must be called at the top level of a component
- They must not be called inside loops, conditions, or nested functions
- Hooks must be used within React functional components or custom Hooks
Custom Hooks
Custom Hooks allow developers to extract and reuse component logic across multiple components. They are regular functions that use built-in Hooks internally and follow the same naming conventions.
Understanding React Hooks is essential for modern React development, as they are now the standard for managing state, lifecycle events, and component behavior in functional components.
UseState and UseEffect
The useState and useEffect Hooks are two of the most essential tools in React for managing state and handling side effects inside functional components. They help build dynamic, responsive applications without relying on class-based components.
What is UseState
useState is a Hook that lets you add local state to functional components. It stores values that may change over time, such as form inputs, toggle flags, counters, or fetched data. When state changes, React re-renders the component to reflect the updated values.
How useState Works
It returns an array with two elements: the current state value and a function to update that value. You can initialize state with any value such as a string, number, boolean, array, or object. When you call the updater function, React triggers a re-render using the new state.
What is UseEffect
useEffect is a Hook used to handle side effects in React components. Side effects are operations like data fetching, subscriptions, timers, or DOM updates that happen after rendering. It runs after every render by default but can be configured to run only on specific changes.
How useEffect Works
It takes a function as its argument that runs after the component renders. You can optionally include a dependency array to control when the effect runs. If the array is empty, the effect runs only once after the first render. If it contains variables, it runs only when those variables change.
Cleaning Up with useEffect
useEffect supports cleanup by returning a function inside the effect. This cleanup function runs before the component is removed or before the effect runs again. It’s useful for cancelling subscriptions, clearing timers, or avoiding memory leaks.
Best Practices
- Keep state as minimal and specific as possible
- Avoid unnecessary re-renders by structuring dependencies correctly
- Use multiple useEffect calls to separate different concerns
- Use cleanup functions to manage resource-intensive effects
Together, useState and useEffect provide a powerful foundation for managing logic and behavior in React functional components, replacing much of the functionality previously handled in class lifecycle methods.
UseRef, UseMemo, and UseCallback
useRef, useMemo, and useCallback are advanced React Hooks that help optimize performance and manage references in functional components. They are essential when working with complex logic, preventing unnecessary re-renders, or accessing DOM elements directly.
What is UseRef
useRef is a Hook that creates a mutable object to store a value that persists across re-renders. It does not trigger a re-render when updated. Common use cases include accessing DOM elements directly or keeping track of previous state values or timers.
When to Use useRef
It’s useful for scenarios where you need to interact with DOM nodes, manage focus, measure element dimensions, or persist values between renders without affecting the UI.
What is UseMemo
useMemo is a Hook that memoizes the result of a computation and re-computes it only when its dependencies change. It helps avoid expensive calculations on every render and is useful for optimizing performance in components that handle large data or complex logic.
When to Use useMemo
It is typically used to cache computed values derived from props or state that don’t need to be recalculated unless the inputs change. This reduces CPU load and improves UI responsiveness.
What is UseCallback
useCallback is a Hook that returns a memoized version of a function. It prevents a function from being re-created on every render unless its dependencies change. This is helpful when passing functions to child components that rely on reference equality for optimization.
When to Use useCallback
It is commonly used to prevent unnecessary re-renders of child components, especially when the function is passed as a prop and the receiving component is memoized or using effects that depend on the function.
Best Practices
- Use useRef for storing mutable values or accessing DOM nodes
- Use useMemo to cache complex computations or derived data
- Use use
Custom Hooks and when to use them
Custom Hooks are reusable functions in React that allow you to extract and share component logic across multiple components. They leverage built-in Hooks to encapsulate behavior and state management, making your code cleaner and more maintainable.
What Are Custom Hooks
Custom Hooks are JavaScript functions whose names start with “use” and that may call other Hooks inside. They enable you to combine related logic—such as data fetching, form handling, or subscriptions—into a single function that can be reused across different components.
Benefits of Using Custom Hooks
- Promotes code reuse and avoids duplication
- Keeps components focused on rendering UI rather than managing complex logic
- Improves readability and organization by separating concerns
- Makes testing logic easier by isolating it from UI
When to Use Custom Hooks
- When multiple components share the same stateful logic
- To abstract complex logic like API calls, event handling, or timers
- To simplify components by moving non-UI logic outside
- When you want to create reusable utilities that fit React’s Hook rules
Rules for Custom Hooks
Custom Hooks follow the same rules as built-in Hooks: they must be called at the top level of a React function and not inside loops, conditions, or nested functions.
By creating custom Hooks, you can build modular, reusable logic that keeps your React codebase scalable and easier to maintain.