React JS Practice Test 2025

React (also known as React.js or ReactJS) is a front-end JavaScript library for creating user interfaces or UI components that is free and open-source. Facebook and a community of individual developers and businesses maintain it. React can be used to create single-page or mobile applications as a foundation. React, on the other hand, is solely concerned with state management and rendering that information to the DOM, so constructing React apps frequently necessitates the usage of extra frameworks for routing and client-side functionality.

React.js is an open-source JavaScript package that is used to create single-page apps’ user interfaces. For web and mobile apps, it’s utilized to manage the view layer. We can also make reusable UI components with React.

To begin, create a new directory for the Login component: Next, open Login.js in a text editor: Create a simple form with a submit button and a username and password entry. Make sure the password input type is set to password:

Open your machine’s terminal and type npm I react Go to your favourite editor, open a new terminal, and run npx create-react-app name-of-project Make sure you have Node.js installed (this should include npm)

React.js is not a framework.

If you’re using controlled components, your form (input) data is controlled by the react state, which means you can clear the value of an input field by assigning the react state the empty string “.

React JS is a frontend framework for handling your application’s user-facing features. It’s not designed to connect to databases or do other backend tasks.

If your React application needs to connect to a MySQL database, or any other server-hosted database, you’ll need to write an API in a backend language like Node.js, PHP, Python, or anything similar to do the connection and backend work and deliver React data (typically in JSON) to manage the frontend.

A ReactJS widget can be made in two different methods. You have the option of using an iFrame or using JavaScript. In any case, double-check that you have everything you need: Start your server to see if your application is up and running.

We can import images in react components in the same way that we do in JavaScript modules, where webpack bundles the image file and returns the image’s final destination. Importing photos that are less than 10,000 bytes delivers a data URI instead of a path to reduce network requests and enhance site speed.

A Promise object is used for handling asynchronous computations, according to Mozilla, and it provides several crucial assurances that are difficult to implement with the callback function (the more old-school method of handling asynchronous code).

Each React component you develop must have a render function associated to it. There’s no getting around it. It’s part of the React component pattern that’s being followed. React is generally thought to be largely a view-based library, despite the fact that it is much more than the view layer. Making the render method apparent to programming with React is the reason for this.

React.js, also known as React or ReactJS, is a JavaScript library for creating a hierarchy of user interface components, or in other words, for rendering UI components. While React Native is a framework for building native applications using JavaScript, it supports both the frontend and server-side. React Native transforms your code into native app components, allowing you to create native mobile apps.

In ReactJS, a constructor is a method that is used to initialize an object’s state and is called automatically during the creation of an object in a class. The constructor is called before the component is mounted in ReactJS, however it is not required in every component.

React Map is a reactive map. A map is a sort of data collection in which data is kept in pairs. It has a one-of-a-kind key. The key must be mapped to the value saved in the map. The map() method creates a new array by invoking a function on each element of the calling array.

React (also known as ReactJS) is a free JavaScript library that is frequently mistakenly referred to as a framework. Because React is a direct rival of major JavaScript frameworks like AngularJS and VueJS, this is the case.

Angular is a Typescript-based Javascript frame, whereas Reactjs is a Javascript library that uses JSX. Angular is commonly used to create complicated enterprise-grade programs such as single- runner apps and progressive web apps, whereas React is commonly used to create UI elements in apps with continually changeable data.

Developers may use React to build massive web applications that can alter data without reloading the page. React’s major goal is to be quick, scalable, and easy to use. It only works on the application’s user interfaces. This relates to the MVC template’s view. It can be combined with other JavaScript libraries or frameworks, such as Angular JS in MVC applications.

The standard method entails setting up MongoDB and a Node.js server (or whatever back-end you like), then connecting the Node.js server to MongoDB (through MongoDB’s JavaScript SDK) and your React client, which runs in the browser, to your Node.js server (via HTTP, express framework could help here). MongoDB -> Browser -> Node.js

Extend the React.Component class to make a React class component. The onChange handler can be used to bind the state of a form component to a form input.

Here are 5 stages to making a React extension.

1. make a react application
2. Modify the manifest.json file under public/manifest.json.
3. Create a build script (script/build.sh) to automate the process.
4. Make changes to package.json
5. Create and open in Chrome (or Edge) Then you’ll get a directory called ‘dist’. Run it in Chrome or Edge as an unpacked extension.

• Step 1: Use the Import method to import the JSON file into your work file.
• Step 2: After importing the JSON file, use the map() method to cycle through all of the files. When constructing a JSON Object file, use an array.

JavaScript is the first thing you should learn. As you begin learning React, having a thorough understanding of the language and its conventions will be quite beneficial. Everything in React is written in JavaScript, from the package managers to the setup to the components and business logic, so mastering it is the first step.

App. js is the first file in any React Native project, and it is where the app development process begins. The contents of this file will be displayed on the mobile device. The folder node modules/ has all of the dependencies (or packages) required to build and run this application.

A React component can be defined using a class component, which is a more advanced means of doing so. It functions similarly to a function that accepts props, but it also takes into account a private internal state as an additional input that controls the returned JSX.

Context is a notion in React.js that allows you to send data down a component tree without having to provide props down to each level manually.

You should know how to write HTML and CSS before you start learning to react. You should be able to write semantic HTML tags, CSS selectors, use classes, implement a CSS reset, box model, reset to border-box, flexbox, construct responsive web apps with media queries, and design a frontend application using HTML and CSS.

Because of its added simplicity and versatility, ReactJS has become extremely popular. It’s even been dubbed “the future of web development” by some. ReactJS is used by around 1,300 developers and 94,000 websites, according to estimates.

Node.js is the best platform for hosting and running a React application’s web server. You can use React JS and Node JS together for two main reasons: with the support of NPM (Node Package Manager), Node works properly with the NPM registry to easily install any package via the NPM CLI.

In a React component, we can clear an input value after it has been submitted. To block the default submit behavior, we use preventDefault. Then we obtain the state’s name, which is what we entered. After that, we use our search function. Finally, the input value is cleared by assigning an empty string to the name state.

It will take you anything from 1 to 12 months to become expert in React. This is dependent on your prior software development experience, javascript expertise, and the learning path you choose.

After submitting a form, a React component can clear an input value. To halt the default submit behavior, we call preventDefault. Then we get the name from the state, which is the same as the one we entered. The search function is then invoked. Finally, by assigning an empty string to the name state, we clear the input value.

There are various ways to declare an array in JavaScript. Let’s look at two of the most frequent methods: array constructors and literal notation. Array objects are created using the Array () constructor. To instantiate an array in memory, use the “new” keyword when declaring it.

It should no longer be difficult to run a JS project on localhost. In truth, all you need to do is install the requirements on your system, learn the fundamental ideas and a few commands, and then execute them correctly. Then you should be able to execute React.js projects locally without difficulty!

It’s vital to remember that React is a JavaScript library, therefore it’s not “faster” than JavaScript when it comes to DOM manipulation. “Faster than JavaScript” isn’t the case with React. React is about as quick as JavaScript, and it’s far more difficult for you to mess it up as a developer.