Frequently Asked Questions about Hooks

Rubleen Kaur
Last Updated: May 13, 2022

Introduction

Hooks in React allows you to hook into the react state and lifestyle features through the function component. Hooks are a new feature update of the React in version 16.81. Hooks allow us to use the functionality of various states and React features without using the class. Hooks allow you to create an entire React Application with just functional components. In this article, we will be discussing the 30 most frequently asked questions on Hooks. We have seen that Hooks are extensively used for reducing the redundancy of the code, and we can even create our custom hooks, which can be used anywhere in the React applications. But, we feel you still might have some questions more? We have written this blog to address the frequently asked questions on Hooks. 

 

Frequently Asked Questions on Hooks

 

  What are React Hooks? 

AnsHooks are in-fabricated capacities that permit developers to utilize state and lifecycle strategies inside components in React. Every part's life cycle has three stages which are mount, unmount, and update. Close by that, and components have states and properties. Hooks permit us to utilize these techniques while further developing code reusability with more prominent adaptability exploring the component tree. Hooks in React enables you to guide into the react state and lifestyle features through the function component. Hooks are another component update of the React in version 16.81. Hooks permit us to utilize the functionality of different states and React highlights without using the class. Hooks allow you to make a whole React Application with simply functional components.

 

Which version of React includes hooks?

Ans: Hooks were introduced with 16.8.0. React includes a stable implementation of  Hooks for:  

→ React DOM

React Native

React DOM Server

React Test Renderer

React Shallow Renderer

If you want to enable Hooks, all React packages need to be 16.8.0 or higher. Hooks won’t work if you do not have the update.

 

What are the two rules you must follow while working with React Hooks?

Ans: Rules we should keep in mind when either creating our hooks and even using the built-in hooks are: 

  1. Hooks should be called from the top of the level. 
  2. Hooks should be called from the React functions.

 

These are the two main rules you should keep in mind before you create or use Hooks. 

List some advantages of React Hooks.

Ans: Few Advantages of Hooks are: 

  1. It makes the code more readable. 
  2. It reduces the code length.
  3. Overall optimization of the components is improved.
  4. We can write a functional component with a state. 
  5. It makes complex writing components much more accessible. 
  6. It handles the events and logic in the available components. 
  7. It boosts the performance with the use of functional components. 

 

What are State Hooks in React?

Ans: The React useState uses this hook to return a current state's value pair and the function to edit or update the value. We can make a call to this function from an event handler or from anywhere else. The ReactJs offers something similar to this setState class, except the hook does not merge the old and the new state after any updates.

 

Should we use Hooks, classes, or a mix of both?

Ans: We cannot use Hooks inside a class component, but you can mix classes and function components with Hooks in a single component tree. Whether we have a component as a class or a function that uses Hooks is an implementation detail of that component. In the longer term, Hooks are expected to be the primary way people write React components.

 

Can we use Hooks in Static Typing?

Ans: Hooks were planned in light of static typing. Since they're functions, which are more straightforward to type accurately than designs like higher-request parts, the most recent Flow and TypeScript React definitions incorporate help for React Hooks. Critically, custom Hooks enable you to compel React API if you'd prefer to type them all the more stringently somehow or another. Respond gives you the natives, yet you can join them in unexpected ways compared to what we offer out of the crate.

 

What is the difference between the setState() method and useEffect() in React?

 Ans: In simple words, the setState() method allows you to set the state of functional components, whereas the useEffect() method allows us to use lifecycle methods in React. 

 

What is the purpose of the useEffect() hook?

Ans: The Effect hook allows us to perform the side effects in the functional components. This helps us to avoid any redundant code in various lifecycle methods of a class component. It helps to group related code.

 

Explain State Hook with an example.

  AnsState Hooks are generally used to refer to the states of the components in React, which can be used to change them on the runtime as per the functionality of your web application. 

Let’s go through an example, to understand better:

import React, { useState } from "react";

 

function CountNinja() {

 // Declaring a new state variable.

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

 

 return (

   <div>

     <p>Ninja clicked {count} times</p>

     <button onClick={() => setCount(count + 1)}>Click me</button>

   </div>

 );

}

export default CountNinja;

 

 

 

How can we use multiple states with Hooks?

Ans: The example below illustrates the use of multiple states with React Hooks: In the given example, we have declared various states within a single function. We have the student, roll number, marks, and name in a single MultipleStates() above.

 

function MultipleStates() {

 // Declare multiple state variables!

 const [student, setrnumber] = useState(19);

 const [student_name, setName] = useState('Coding Ninjas');

 const [marks, setmarks] = useState(75);

 // ...

}

 

 

Explain Effect Hooks with Example.

 

AnsIf an action is performed on a webpage, the Effect Hook transfers a side effect to another part of the DOM. The example below updates the document title of the webpage when a button is clicked:

Let’s go through an example to understand the React Hooks better:

 

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

 

const App = () => {

 const [message, setMessage] = useState("Hi Ninja, how are you?");

 

 useEffect(() => {

   console.log("This is a trigger use effect hook");

 

   setTimeout(() => {

     setMessage("We hope you are doing great! Bye :)");

   }, 2000);

 });

 

 return <h1>{message}</h1>;

};

 

export default App;

 

             OUTPUT

 

 

Can Hooks replace render props and higher-order components?

Ans: The render props and higher-order components render only a single child. We know that Hooks are an easier way to serve this problem. We can still use a place for both patterns (for example, when we implement a virtual scroller component we might have a renderItem prop, or a visual container component might have its DOM structure). So yes, hooks can replace the render props and higher-order components in React.

 

Why does the useState Hook not update immediately?

AnsReact useState, and setState don't make any changes directly to the state object; but they create queues that optimize the performance; that is why the changes don't update immediately at times. 

 

Do Hooks become slow as they create functions in render?

Ans: No hooks do not slow down. In browsers, the raw performance of closures compared to classes does not differ significantly except in extreme scenarios.

We believe the design of Hooks is more efficient in a couple of ways:

  • Hooks can avoid a lot of the overhead that classes require, like the cost of creating class instances and binding event handlers in the constructor.
  • Idiomatic code using Hooks doesn’t need the deep component tree nesting that is prevalent in codebases that use higher-order components, render props, and context. With smaller component trees, React has less work to do.

Let’s consider this example,

 

// Will not change unless `a` or `b` changes.

 

const memoizedCallback = useCallback(() => {

 doSomething(a, b);

}, [a, b]);

 

 

Why is React Hooks better?

Ans:  Using Hooks, we can extract stateful logic from a component that can be tested solely and reused. Hooks allow us to reuse stateful logic without modifying our component hierarchy. By this, it has been made easy to share Hooks among many components or with the community. 

 

What is a Custom Hook in React?

Ans: Custom hooks are general essential functions with the keyword “use” before their identifier.  The customized hook is just like a regular function, and the word "use" in the beginning tells us that this function follows the rules of Hooks. Building custom Hooks allows us to extract component logic into reusable parts, but every time we use a custom Hook, all states and effects inside of it are fully isolated.

 

If the two components share the same hook, would they share the same state?

Ans: No. Custom Hooks are a method that is used to reuse stateful logic (such as setting up a subscription and remembering the current value). Still, whenever we use a custom Hook, all states and effects inside it get fully isolated.

 

How does a custom hook get an isolated state?

Ans: In React, Each call to a Hook takes us into an isolated state. This is because when we call a custom hook directly, our component just calls state and useEffect. We can call useState and useEffect any number of times in one component, and they will be completely independent.

 

How can we memoize calculations in Hooks?

Ans: To memorize the calculations, we can use the useMemo hook. It allows us to cache calculations between multiple threads by remembering the previous computation. The given code calls computeExpensiveValue(a, b). But if the dependencies [a, b] have not been changed since the last value, useMemo skips calling it a second time and reuses the last value the method returned.

 

const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

How are custom hooks different from general functions?

Ans:  A custom hook is a function that follows the rules of hooks, just like built-in hooks. Since the custom hooks typically contain hooks themselves, we have to make sure our custom hooks are only called where it is legal to use hooks generally. The difference between a general function and a custom hook is that the custom hooks start with the keyword ‘use’. 

How do we pass props in Hooks?

Ans: We can pass props easily to hooks by passing them in states using the useState method for the same. 

 Explain the useCallback Hook using an example. 

Ans: The useCallback Hook in react allows us to pass an inline callback function and an array of dependencies that will return a memoized version of the callback function. The useCallback Hook in react is useful when passing callbacks to optimized child components. It works similarly to the useMemo Hook, only for callback functions. We can apply it as follows:

Example:

import { useCallback } from 'react'

const memoizedCallback = useCallback(

    () => {

       work(a, b)

    },

    [a, b] )

 

Name the three basic React Hooks.

Ans: React Basic Hooks present the most commonly required functionalities in stateful React apps. They are as follows:

  1. React useState
  2. React useEffect
  3. React useContext

 

What are the benefits of using React Hooks?

Ans: Hooks offer a lot of benefits to the developers. They make our component better, and it helps in writing clear, concise, and maintainable code. It just cuts all the unnecessary code from your component and makes your code more readable. But the question is when to use React hooks? Use Hooks when you're writing a function component, and you want to add some state to it. Earlier this job was done by using a Class, but now you can write the hooks inside a function component. 

 

Key Takeaways

Hey everyone, so let’s brief out the article. Let’s discuss in brief whatever we have discussed here. We have discussed the top 25 frequently asked questions on Hooks. These frequently asked questions on hooks are aimed to be a key for developers like you. We hope you have your queries clear now. So go on, the sky's the limit, remember to create something amazing from your understanding, and post your applications. 

 

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Happy Learning Ninjas!

 

By: Rubleen Kaur

 

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