Everything You Need to Know About React Hooks in Just 1 Hour | Common React JS Hooks Interview Questions | Quick React Hooks Crash Course

React Hooks have become an essential part of building modern, efficient, and scalable applications with React. They provide a way to add stateful logic to functional components without the need for classes. In this tutorial, we will cover all the React hooks and explain each one in detail in just one hour. We will also go through some common interview questions related to React hooks, and provide a crash course on how to use them.

Before we start, make sure you have a basic understanding of React and functional components. If you’re new to React, I recommend going through the official React documentation to get a better grasp of the fundamentals.

1. useState

The useState hook allows us to add state to functional components. It takes an initial value as an argument and returns an array where the first element is the current state value, and the second element is a function to update that value.

import React, { useState } from 'react';

const Counter = () => {
  const [count, setCount] = useState(0);

  const increment = () => {
    setCount(count + 1);
  }

  return (
    <div>
      Count: {count}
      <button onClick={increment}>Increment</button>
    </div>
  );
}

1. useEffect

The useEffect hook allows us to perform side effects in functional components. It takes a function as an argument, which will be executed after every render. It can also take a second argument, an array of dependencies, to control when the effect is triggered.

import React, { useEffect, useState } from 'react';

const Counter = () => {
  const [count, setCount] = useState(0);

  useEffect(() => {
    console.log('Count changed:', count);

    return () => {
      console.log('Cleanup');
    };
  }, [count]);

  const increment = () => {
    setCount(count + 1);
  }

  return (
    <div>
      Count: {count}
      <button onClick={increment}>Increment</button>
    </div>
  );
}

1. useContext

The useContext hook allows us to access the context values in functional components. It takes the context object created by React.createContext as an argument and returns the current context value.

import React, { useContext } from 'react';
import MyContext from './MyContext';

const MyComponent = () => {
  const value = useContext(MyContext);

  return <div>Context value: {value}</div>;
}

1. useReducer

The useReducer hook allows us to manage state transitions in more complex scenarios. It takes a reducer function and an initial state as arguments, and returns the current state and a dispatch function to update the state.

import React, { useReducer } from 'react';

const initialState = { count: 0 };

const reducer = (state, action) => {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    default:
      return state;
  }
};

const Counter = () => {
  const [state, dispatch] = useReducer(reducer, initialState);

  const increment = () => {
    dispatch({ type: 'increment' });
  }

  return (
    <div>
      Count: {state.count}
      <button onClick={increment}>Increment</button>
    </div>
  );
}

1. useRef

The useRef hook allows us to access DOM elements or store mutable values within a functional component. It returns a mutable ref object with a current property that can be assigned to a DOM element.

import React, { useRef } from 'react';

const MyComponent = () => {
  const inputRef = useRef(null);

  const focusInput = () => {
    inputRef.current.focus();
  }

  return (
    <div>
      <input ref={inputRef} type="text" />
      <button onClick={focusInput}>Focus Input</button>
    </div>
  );
}

1. useMemo

The useMemo hook allows us to optimize performance by memoizing expensive calculations inside a functional component. It takes a function and an array of dependencies as arguments, and returns the memoized value.

import React, { useMemo } from 'react';

const MyComponent = ({ a, b }) => {
  const result = useMemo(() => {
    return a + b;
  }, [a, b]);

  return <div>Result: {result}</div>;
}

1. useCallback

The useCallback hook allows us to memoize callback functions in functional components to prevent unnecessary re-renders. It takes a callback function and an array of dependencies as arguments, and returns a memoized callback.

import React, { useState, useCallback } from 'react';

const MyComponent = () => {
  const [count, setCount] = useState(0);

  const increment = useCallback(() => {
    setCount(count + 1);
  }, [count]);

  return (
    <div>
      Count: {count}
      <button onClick={increment}>Increment</button>
    </div>
  );
}

These are the basic and most commonly used hooks in React. There are also other hooks like useLayoutEffect, useImperativeHandle, useDebugValue, etc., but those are less commonly used.

Now, let’s quickly go through some common interview questions related to React hooks:

1. What are React hooks?
2. What are the differences between useState and useReducer?
3. How do you perform side effects in React functional components?
4. How do you share state between components using React hooks?
5. How do you optimize performance using React hooks?

Finally, let’s summarize what we’ve learned in this crash course on React hooks:

1. useState: Adds state to functional components.
2. useEffect: Performs side effects in functional components.
3. useContext: Accesses context values in functional components.
4. useReducer: Manages state transitions in complex scenarios.
5. useRef: Accesses DOM elements or stores mutable values.
6. useMemo: Memoizes expensive calculations for performance optimization.
7. useCallback: Memoizes callback functions to prevent unnecessary re-renders.

I hope this tutorial has provided you with a good understanding of React hooks and how to use them effectively in your applications. Remember to practice and experiment with them to get a better grasp of their capabilities. Happy coding!