Sunday, July 7, 2024

React Ui Developer Interview Questions

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What Are The Rules You Should Follow For The Hooks In React

Cognizant interview questions for experienced 2021 | UI Developer | Web Developer |React Js

We have to follow the following two rules to use hooks in React:

  • You should call hooks only at the top level of your React functions and not inside the loops, conditions, or nested functions. This is used to ensure that hooks are called in the same order each time a component renders, and it also preserves the state of hooks between multiple useState and useEffect calls.
  • You should call hooks from React functions only. Don’t call hooks from regular JavaScript functions.

What Are Controlled Components

A component that controls the input elements within the forms on subsequent user input is called Controlled Component, i.e, every state mutation will have an associated handler function.

For example, to write all the names in uppercase letters, we use handleChange as below,


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Explain In Detail The Lifecycle Methods Of React Components

Some of the most important lifecycle methods are:

  • componentDidMount – executed on the client-side only after the first render.
  • shouldComponentUpdate – Returns true or false depending on certain conditions. If you want your component to update, return true, otherwise return false. Returns false by default.
  • componentDidUpdate – called immediately after rendering.
  • componentWillUnmount – Called after the component has been unmounted from the DOM. It is used to clean up memory space.

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When Do You Use React Context Vs Redux

Redux is probably the most commonly used third-party global state library for React, but you can replace the word “Redux” with any global state library for React.

React context is a way to provide and consume data throughout our application without using props.

React context helps us prevent the problem of “props drilling“, which is when you are passing data with props through components that don’t need it.

Instead, with context we can consume the data exactly in the component that needs it.

While we only use Context to get or “read” values globally in our application, Redux and other third-party state libraries allow us to both read and update state.

Context is not a replacement for a third-party state library like Redux because it is not built for state updates. This is because any time the value provided on Context changes, all of its children will re-render, which can hurt performance.

Can Ajax Be Used With React

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Yes, any AJAX library, such as Axios and jQuery AJAX, can be used with React easily. One important thing is to maintain the states of the components, and here too, the props are passed from the parents to the child components.

Child components still cannot send back props to parents, and this factor greatly increases rendering efficiency when dynamic data is considered.

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Ui Developer Interview Faqs

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 .

What Are The Advantages Of Jest Over Jasmine

There are couple of advantages compared to Jasmine:

  • Automatically finds tests to execute in your source code.
  • Automatically mocks dependencies when running your tests.
  • Allows you to test asynchronous code synchronously.
  • Runs your tests with a fake DOM implementation so that your tests can be run on the command line.
  • Runs tests in parallel processes so that they finish sooner.
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    What Is The Difference Between Mapstatetoprops And Mapdispatchtoprops

    mapStateToProps is a utility which helps your component get updated state :

    constmapStateToProps==> }

    mapDispatchToProps is a utility which will help your component to fire an action event :

    constmapDispatchToProps==> }}

    It is recommended to always use the object shorthand form for the mapDispatchToProps.

    Redux wraps it in another function that looks like => dispatch), and pass that wrapper function as a prop to your component.


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    How Can We Handle Asynchronous Code

    Frontend Interview Experience (Unacademy) – Javascript and React JS Interview Questions

    Why this question: This question checks not only if but also in what ways candidates know how to handle async operations.

    Answer: There are several ways to handle asynchronous code in javascript: callbacks, Promises, and async/await. Initially, such operations were handled by callbacks, i.e. functions that are called when the result of our asynchronous operation is ready. Unfortunately, the code often becomes unreadable when it is necessary to execute one asynchronous operation after another .

    Promises work similarly to callbacks, but we have a few differences here. First, we dont need to add a callback to Promise, Promise has its own functions that are called when our operation succeeds or fails. The second difference is the ability to chain dependent asynchronous operations instead of nesting consecutive callbacks as in the case of the first method.

    Async / await is syntactic sugar on promises which makes asynchronous code look more like synchronous which is more readable to the programmer. The code is actually handled in the same way as in the case of regular promises.

    Best answer*: The candidate should be able to provide an example of an asynchronous operation and describe how to handle errors in the listed asynchronous code handling methods. Its best if you know how to perform several such operations at the same time.

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    How Do You Create Hoc Using Render Props

    You can implement most higher-order components using a regular component with a render prop. For example, if you would prefer to have a withMouse HOC instead of a component, you could easily create one using a regular with a render prop.

    functionwithMousemouse=/> )}/> ) }}}

    This way render props gives the flexibility of using either pattern.

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    Explain Mixin Or Higher Order Components In React

    A: HOC in React are functions that take and return components. Basically, it reuses component logic. That being said, you should also know that HOC isnt exactly a part of React API. They are functions that loop over and apply functions to every element in an array. Keep that in mind when answering React js questions.

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    Programming Basics React Interview Questions

    Why to ask these React interview questions:

    You should interview your candidate on programming basics to make sure that he doesnt only build monotonous forms but is curious about programming in general, emerging technologies, and new tech challenges. After all, if you want them to develop their expertise, you need to make sure that they want it to, and the basic knowledge of programming proves it. Since there are many interview questions for a react developer to ask, it would be better to include the following ones as well:

    Interview Questions With Sample Answers

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    Below are common ReactJS interview questions and example answers:

    • Explain components in React.

    • Why are components so important?

    • Explain the differences between props and state.

    • Describe an instance where a class component would be used.

    • Tell me about an instance when a functional component would be used.

    • Can you define reactive events?

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    What Is An Arrow Function In React How Is It Used

    Arrow functions are a shorter syntax for writing a function expression. They are also called bold arrow functions. These functions allow you to bind the component context correctly, as in ES6, automatic binding is not available by default. Arrow functions are mostly useful when dealing with higher-order functions.

    What Are The Popular React

    ESLint is a popular JavaScript linter. There are plugins available that analyse specific code styles. One of the most common for React is an npm package called eslint-plugin-react. By default, it will check a number of best practices, with rules checking things from keys in iterators to a complete set of prop types.

    Another popular plugin is eslint-plugin-jsx-a11y, which will help fix common issues with accessibility. As JSX offers slightly different syntax to regular HTML, issues with alt text and tabindex, for example, will not be picked up by regular plugins.

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    What Is A Consumer

    A Consumer is a React component that subscribes to context changes. It requires a function as a child which receives current context value as argument and returns a react node. The value argument passed to the function will be equal to the value prop of the closest Provider for this context above in the tree.

    Lets take a simple example,

    < MyContext.Consumer> < /MyContext.Consumer> 

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    What Is The Purpose Of Forward Ref In Hocs

    Accenture interview questions and rounds for UI developer | Reactjs developer

    Refs will not get passed through because ref is not a prop. It is handled differently by React just like key. If you add a ref to a HOC, the ref will refer to the outermost container component, not the wrapped component. In this case, you can use Forward Ref API. For example, we can explicitly forward refs to the inner FancyButton component using the React.forwardRef API.

    The below HOC logs all props,

    functionlogPropsrender=this.props // Assign the custom prop "forwardedRef" as a refreturn< Componentref=/> }}returnReact.forwardRef=> forwardedRef=/> }) }

    Let’s use this HOC to log all props that get passed to our fancy button component,

    classFancyButtonextendsReact.Component// ...}exportdefaultlogProps 

    Now let’s create a ref and pass it to FancyButton component. In this case, you can set focus to button element.

    importFancyButtonfrom'./FancyButton' constref=React.createRef ref.current.focus < FancyButtonlabel="Click Me"handleClick=ref=/> 

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    What Is React Js

    Tip: OK, BASIC sounding question,but thats the thing: its so basic you might not have a succinct definition handy. And thats exactly why interviewers ask this simple but telling question. Here are a few quick points to cover:

    • React JS is a front end JavaScript library for building web and mobile user interfaces
    • It was developed by Facebook in 2011
    • React allows developers to build reusable UI components
    • It has the support of a large, open source community

    How Does Context Api Work In React

    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 Are Error Boundaries

    A JavaScript error in one part of the app shouldnt break the entire app. Error boundary is Reacts solution to this common problem. The candidate should be able to explain what an error boundary is and to use it to handle errors in your application.

    Error boundaries are React components that catch JavaScript errors anywhere in its child component tree. The Error boundary component can then log those errors and display fallback UI instead of crashing the entire component tree. You can think of error boundaries as a catch block for components.

    The snippet below shows a simple ErrorBoundary component that displays a fallback h1 and logs the error.

    classErrorBoundaryextendsReact.Component    }staticgetDerivedStateFromError    }componentDidCatch render return this.props.children    }}

    The ErrorBoundary component can then be used to catch all errors in the Child component as follows:

    < ErrorBoundary> < Child /> < /ErrorBoundary> 

    How Do You Understand The Concepts Of Mvc Mvp Mvvm

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    What answer to expect:

    MVC is a software development pattern, which stands for Model, View, Controller.

    MVP is a software development pattern, which stands for Model, View, Presenter.

    MVVM MVC is a software development pattern, which stands for Model, View, View Model.

    Models contain all the application data. Views display visual elements and controls on the user interface. Controller takes inputs and converts it into commands for Model or View. Presenter acts as a middleman between Model and View it takes data from Model and formats it to be displayed by View. A View Model transforms data from Model into values that View can display.

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    Is Setstate Async Why

    A: setState actions are indeed asynchronous. setState doesnt immediately mutate this.state. Instead, it creates a pending state transition. Accessing this.state after calling this method can potentially return the existing value. There is no guarantee of synchronous operation of calls to setState and calls may be batched for performance gains.

    The reason behind is the way setState alters the state and causes rerendering. Making it synchronous might leave the browser unresponsive. That being said, the setState calls are asynchronous as well as batched for better UI experience and performance. Keep this in mind as this is definitely among the most popular 50 interview questions and answers when it comes to React.

    What Is The Difference Between A Document And A Window

    The window is the first thing that loads into the browser. It has properties like inner width, inner height, length, name.

    The Document gets loaded inside the window object. It is similar to HTML, PHP, and other documents which are loaded into the browser and have properties like title, URL, cookies, etc.

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    What Are Some Of The Advantages Of Using Create

    Making use of create-react-app is advantageous in the following way:

    • Support for JSX, ES6, and flow statements
    • Already built and ready auto-prefixed CSS
    • Fast interactive testing components
    • Live development servers that help in debugging
    • Scripts to handle JSS, CSS, and other files

    Next up on these React Redux interview questions, you need to understand the meaning of Redux.

    What Is React State And How Is It Implemented

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    State refers to data that is associated with a component that may change, thus causing a re-render of that component. It can be used to create highly interactive UI elements that update at the press of a button.

    State is often used to handle and render data from APIs, complement complex CSS, and determine how an element is rendered.

    State is handled in React most commonly through the React hook useState. It can be used to establish some data associated with any given component that may be updated, also through the useState hook.

    Class components were once the only way to have stateful components. Due to React hooks, however, functional components have become a more succinct, developer-friendly method for implementing state.

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    What Frameworks Do You Work With

    Frameworks provide a structure in which software engineers can build programs for a specific platform. Frameworks are needed when code for an application or program seems to have zero structure and rough functionality, because as frameworks, they mandate how your code is structured and how it will run. Thats why interviewers often mention frameworks in senior front end developer interview questions.

    Sample questions:

    • What is React used for?
    • What are the advantages and disadvantages of Virtual DOM?
    • Are TSX and JSX the same?
    • How do props work in React?
    • What are Hooks in React?
    • What is NextJS used for?

    What Are Custom Hooks

    A Custom Hook is a function in Javascript whose name begins with use and which calls other hooks. It is a part of React v16.8 hook update and permits you for reusing the stateful logic without any need for component hierarchy restructuring.

    In almost all of the cases, custom hooks are considered to be sufficient for replacing render props and HoCs and reducing the amount of nesting required. Custom Hooks will allow you for avoiding multiple layers of abstraction or wrapper hell that might come along with Render Props and HoCs.

    The disadvantage of Custom Hooks is it cannot be used inside of the classes.

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    What Is A React Fragment

    A common practice when returning multiple elements in a React Component is to wrap them together using a < div> . React Components require that all Components return only one element, and so this is the instinctual solution.

    function DivExample 

    However, React provides Fragments, essentially empty HTML tags < > < /> . These can wrap multiple elements while not actually rendering another div in the frontend, making much cleaner code.

    function FragmentExample 

    Whats Your Experience With Javascript

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    With modern web apps, front end development is much more than just building user interfaces its also about implementing HTML5 technologies. Without a solid understanding of asynchronous JavaScript in particular, or pure JavaScript in general, you will have trouble understanding some powerful HTML5 APIs like Web Workers, WebSocket, WebRTC, and IndexedDB.

    More importantly, engineers with poor knowledge of JavaScript often write unmaintainable code. So while preparing for the front end developer interview, ensure you know the answers to the questions below, whether you work with pure JavaScript or are interviewed for a company hiring React.JS developers, for example.

    Sample questions:

    • Explain the difference between synchronous and asynchronous functions.
    • Why is fetch the preferred way to send a network request via the browser?
    • If the browser encounters malformed HTML, what happens?
    • Is there another option, besides explicit promises, to handle asynchronous code in JavaScript?
    • Explain the function and syntax of the array forEach method.
    • Explain the function and syntax of the function bind method.
    • Is there a way to stop an event from bubbling up?
    • How is the event loop defined in the JavaScript engine?
    • How do callbacks work in JavaScript?
    • What design patterns do you know?

    JavaScript interview questions at EPAM Anywhere: everything you need to know

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