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Interview Questions For React Developers

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Should I Learn Es6 Before Learning Reactjs

React.JS Mock Interview | Interview Questions for Senior React.JS Developers

No, you dont have to learn es2015/es6 to learn react. But you may find many resources or React ecosystem uses ES6 extensively. Let’s see some of the frequently used ES6 features,

  • Destructuring: To get props and use them in a component
    // in es 5varsomeData=this.props.someDatavardispatch=this.props.dispatch// in es6const=this.props
  • Spread operator: Helps in passing props down into a component
    // in es 5< SomeComponentsomeData=dispatch=/> // in es6< SomeComponent/> 
  • Arrow functions: Makes compact syntax
    // es< /li> })// es 
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    Reactjs Interview Questions And Answers For 2022

    Latest posts by Aran Davies

    Whether youre an entrepreneur, a project manager in a large enterprise, or a CTO, you are well aware that the success of your project rests on your ability to find top developers.

    In this guide, youll find example interview questions and answers you can refer to when seeking a new ReactJS developer to make your dynamic user interfaces come to life. Youll also get some practical advice on how to use these questions to reliably identify the best developers for the job.

    What Are Pure Functional Components

    Traditional React Components as we have seen so far are making a class with class Example extends React.Component or React.createClass. These make stateful components on the off chance that we at any point set the state , getInitialState, or this.state = inside a constructor).

    In the event that we have no expectation for a Component to require state, or to require lifecycle methods, we can really compose Components with a pure function, consequently the expression “pure function Component”:

    function Date = propslet now = new Datereturn < div> < span>  < /span> < time>  < /time> < /div> }

    This function that returns a React Element can be used wherever we see fit:


    You might notice that also takes a prop â we can still pass information into the Component.

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    What Is The Useeffect Hook Used For

    The useEffect hook is used for performing side effects in our React components.

    Side effects are operations that are performed with the “outside world” or something that exists outside the context of our React app.

    Some examples of side effects include making a GET or POST request to an external API endpoint or working with a browser API like window.navigator or document.getElementById.

    We cannot perform operations like these directly within the body of our React component. useEffect gives us a function within which to perform side effects and a dependencies array which lists any external values that the function relies upon.

    If any value within the dependencies array changes, the effect function runs again.

    What Is React How Is It Different From Other Js Frameworks


    Although this sounds like a relatively simple question, its really asking the candidate to state an informed opinion about React, as well as any competing alternatives. In short, this question is designed to test a candidates knowledge about the JavaScript ecosystem at large while also pressing for specifics on what makes React unique.

    Lets look at each part of the answer separately.

    What is React?

    React is an open-source JavaScript library created by Facebook for building complex, interactive UIs in web and mobile applications.

    The key point in this answer is that Reacts core purpose is to build UI components it is often referred to as just the V in an MVC architecture. Therefore it has no opinions on the other pieces of your technology stack and can be seamlessly integrated into any application.

    How is React different?

    The answer to this question will likely vary depending on the candidates personal experiences. The important thing is to listen for real-life examples provided and opinions on whether or not the candidate prefers React and why.

    Because React is a small library focused on building UI components, it is necessarily different than a lot of other JavaScript frameworks.

    I recently migrated an application originally written in Angular to React, and one of the things I loved most was

    Be prepared to answer some follow-up questions as well, such as:

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    How Can You Protect Your App From Xss

    What answer to expect:

    To conduct a cross-site scripting attack, one injects a piece of malicious code, which runs a client-side script, into a legitimate web page. Once a user opens the infected website, the users browser downloads the script. To prevent an XSS attack, you should encode all variable strings before they will be displayed on the web page. In other words, you should convert every potentially dangerous character to an HTML entity. Also, you should limit input by types: a user can type only numbers into a number field and so on.

    How To Setup React Js

    When you create react app using create-react-app App_name that time generate some folders like as: build/, node_modules/, public/, src/, .gitignore/,, package-lock.json,Package.json.

    In these folders, some folders or files are not useable. Such as, .gitignore, package-lock.json and in a public folder, this file is not usable: favicon.ico, logo192.png, manifest.json, logo512.png, robots.txt. Replace your files with this file and use.

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    What Is The Difference Between React Native And React

    React is a JavaScript library, supporting both front end web and being run on the server, for building user interfaces and web applications.

    React Native is a mobile framework that compiles to native app components, allowing you to build native mobile applications in JavaScript that allows you to use React to build your components, and implements React under the hood.

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    What Is An Action In Redux

    React Native Mock Interview | Interview Questions for Senior React Native Developers

    Actions are plain JavaScript objects or payloads of information that send data from your application to your store. They are the only source of information for the store. Actions must have a type property that indicates the type of action being performed.

    For example, let’s take an action which represents adding a new todo item:


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    Why Did You Choose To Work With React

    Tip: This kind of question is less about rattling off facts related to JSX, Virtual DOMs, props, or state, and more about explaining to an employer why you have a professional interest in working with React JS. One of the main reasons this question is of interest to an interviewer is because it gives a sense of how you might explain the importance of using React to a non-technical client or stakeholder.

    To answer, simply think of what drew you to React JS. It can be something as basic as the fact that React is easy to learn and start with, but allows plenty of room for growth over time , or something as practical as the fact that there are so many job opportunities for React developers .

    Why Function Is Preferred Over Object For Setstate

    React may batch multiple setState calls into a single update for performance. Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state.

    This counter example will fail to update as expected:

    // Wrongthis.setState

    The preferred approach is to call setState with function rather than object. That function will receive the previous state as the first argument, and the props at the time the update is applied as the second argument.

    // Correctthis.setState=> )

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    When Do We Prefer To Use A Class Component Over A Function Component

    If a component needs state or lifecycle methods, we should use the class component otherwise, use the function component. However, after React 16.8, with the addition of Hooks, you could use state, lifecycle methods, and other features that were only available in the class component right in your function component.

    Ui Developer Interview Faqs

    Top 50 React Interview Questions and Answers For 2021

    Q. How do I prepare for my UI developer interview?A. UI developer interviews vary across levels in the company and regions, so you should start by visiting the career or job openings page on their website and understand the role requirements. You could also sign up for a technical interview preparation course where experts will guide you through the technical interview process at FAANG companies.

    Q. What is the career scope of a UI developer?A. A UI developer can gain some experience to become an IT project manager. If you are a UI developer with experience and want to move to a management role, you need to develop skills such as relationship building, working in a team, communication, and motivating and influencing others.

    Q. What is the average salary of a senior UI developer in the U.S.?A. On average, a UI Developer in the US earns around $119,224 .

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    What Is Idempotence And How It Is Connected With Fp

    What answer to expect:

    Idempotence is a concept used in mathematical logic and computer science. Simply saying, it means that the same operation should always return the same output if provided the same input. Its relation with the Functional Programming rests in the fact that the concept of idempotence reflects one of the core principles of FP, that is, Pure functions.

    How To Debug Forwardrefs In Devtools

    React.forwardRef accepts a render function as parameter and DevTools uses this function to determine what to display for the ref forwarding component.

    For example, If you don’t name the render function or not using displayName property then it will appear as ForwardRef in the DevTools,

    constWrappedComponent=React.forwardRef=> forwardedRef=/> }) 

    But If you name the render function then it will appear as ForwardRef

    constWrappedComponent=React.forwardRefforwardedRef=/> }) 

    As an alternative, You can also set displayName property for forwardRef function,

    functionlogPropsfunctionforwardRefforwardedRef=/> }// Give this component a more helpful display name in DevTools.// e.g. "ForwardRef)"constname=Component.displayName|| forwardRef.displayName=`logProps` returnReact.forwardRef }

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    What Are Some Of The Major Advantages To Using React When Building Uis

    Tip: Employers want to know thatwhile you know how to use Reactyou also know WHY React is such a useful tool in the development process. Some of the major advantages of using React include:

    • Increased application performance via the Virtual DOM model
    • Improved coding efficiency with JSX
    • The ability to reuse components across multiple projects
    • Flexibility and extensibility through add-on tools provided by Reacts open source community

    How Does Context Api Work In React

    REAL React Interview Questions

    What answer to expect:

    Usually, variables have to be passed from parent nodes to child nodes, which may be a cumbersome solution. Context is a way to share this data without passing it explicitly through each level of a tree. Context passes the data from a parent to every child of it, which is marked as a context consumer. In other words, a parent is a context provider, and each child that agrees to accept changes in context is a context consumer. For example, context is often used to set UI themes, which are used in most, if not all, parts of the app.

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    What Is A Virtual Dom

    A virtual DOM is what React uses under the hood. Virtual DOM is an implementation of the Document Object Model. The DOM is a tree structure representation of all the elements on a webpage. The tree structure is used to store all the information related to a webpage. Generally, the DOM is stored in memory or in the browser’s cache. The application accessed the DOM from the browsers cache and updated the DOM whenever something changes. This was a slow process and so, the DOM was called a painful DOM. Virtual DOM speeds up the DOM by making a copy of the DOM in memory and then comparing it with the original DOM. When there is a difference, the virtual DOM quickly updates only the changed elements, instead of the entire DOM.

    Explain The Purpose Of Render In React

    It is mandatory for each React component to have a render function. Render function is used to return the HTML which you want to display in a component. If you need to rendered more than one HTML element, you need to grouped together inside single enclosing tag such as < div> , < form> , < group> etc. This function returns the same result each time it is invoked.

    Example: If you need to display a heading, you can do this as below.

    Points to Note:

    • Each render function contains a return statement.
    • The return statement can have only one parent HTML tag.

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    Why Are Redux State Functions Called Reducers

    Reducers always return the accumulation of the state . Therefore, they act as a reducer of state. Each time a Redux reducer is called, the state and action are passed as parameters. This state is then reduced based on the action, and then the next state is returned. You could reduce a collection of actions and an initial state on which to perform these actions to get the resulting final state.

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    What Is Brute Force And How To Avoid It Have You Heard About Salt And Pepper Terms

    Full Stack Developer Technical Interview Questions And Answers (React ...

    What answer to expect:

    When somebody conducts a brute-force attack, they submit numerous passwords with the hope to eventually guess correctly. This attack can be used to break into a closed-access system or account or to decipher encrypted data. It is often used when the attacker sees no other weaknesses that they may tackle to breach the system. The simplest way to prevent brute-force attacks is to limit the number of failed login attempts. Using Captcha or two-factor authentication may also help.

    As for salt and pepper, it is a password hashing terminology.

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    What Do You Know About Flux

    Basically, Flux is a basic illustration that is helpful in maintaining the unidirectional data stream. It is meant to control construed data’s unique fragments to make them interface with that data without creating issues. Flux configuration is insipid it’s not specific to React applications, nor is it required to collect a React application. Flux is basically a straightforward idea, however, you have to exhibit a profound comprehension of its usage.

    What Do You Understand From In React Everything Is A Component

    In React, components are the building blocks of React applications. These components divide the entire React application’s UI into small, independent, and reusable pieces of code. React renders each of these components independently without affecting the rest of the application UI. Hence, we can say that, in React, everything is a component.

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    Explain Css Module Styling In React

    CSS Module is a CSS file where all class names and animation names are scoped locally by default. It is available only for the component which imports it, and without your permission, it cannot be applied to any other Components. You can create CSS Module file with the .module.css extension.

    For More Information, .

    What Is The Concept Of Keys In React And Why Cannot We Use Indexes Of The Map As Keys For Dynamic Lists

    IBM ReactJs Interview – Fresher | ð Selected | ReactJs & Javascript #reactinterviewquestions #ibm

    What answer to expect:

    Keys are the properties given to every element in an array to give them a unique ID and identify which items have changed . Keys have to be static and unique. Meanwhile, a map is an iterative function. If we used map indexes as keys for dynamic lists, then the entire list would be rerendered once a change in a single element occurred.

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    Is It Good To Use Arrow Functions In Render Methods

    Yes, You can use. It is often the easiest way to pass parameters to callback functions. But you need to optimize the performance while using it.

    classFooextendsComponentrender> Click Me< /button> }}

    Note: Using an arrow function in render method creates a new function each time the component renders, which may have performance implications

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    List Down The Advantages Of React Router

    Few advantages are:

  • Just like how React is based on components, in React Router v4, the API is All About Components. A Router can be visualized as a single root component in which we enclose the specific child routes .
  • No need to manually set History value: In React Router v4, all we need to do is wrap our routes within the < BrowserRouter> component.
  • The packages are split: Three packages one each for Web, Native and Core. This supports the compact size of our application. It is easy to switch over based on a similar coding style.
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    What Are The Features Of Reactjs

    The features of React JS are as follows:

    1. React improves SEO performance

    React boost the performance of the SEO to higher levels as a search engine faces the problem while reading JavaScript of high-loaded applications.

    2. React acts as a standard for mobile app development

    It provides a transition process as an ideal solution for both mobile and web applications for building rich user interfaces.

    3. React makes the process of writing components easier

    Using React along with JSX will make you write components and code efficiently and clearly.

    4. React increases efficiency

    React boost the efficiency of components by reusing them. This is the reason why it is considered an ideal feature of React. It is considered the most reusable system component.

    5. React ensures stable code

    It ensures the stability of the code of an application by making use of downward data flow.

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    How Can You Resolve Common React Native Performance Issues

    How I landed a React developer job during my #100DaysOfCode challenge

    Sample answer:

    When performance issues occur, there are several solutions available to developers. For example, here are some solutions for a few common performance issues:

    • High CPU usage: Optimizing apps by compressing data, cutting out wasteful renders, and using cache storage will improve performance speed
    • Memory leak: Memory leak can be avoided by debugging, avoiding the use of console statements, and regularly checking code for inconsistencies
    • Slow navigation: Using React Navigation instead of other navigation tools like Navigator or NavigationExperimental will help soothe navigational issues

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