200+ UI Developer Interview Questions and Answers

Create 10 checkboxes in JavaScript and display the count of checked checkboxes below. Update count on unchecking.

• Use JavaScript to create checkboxes

• Add event listener to checkboxes to track changes

• Update count of checked checkboxes on change

• Display count below checkboxes

Redux is a predictable state container for JavaScript apps.

• Redux is a state management library for JavaScript applications.

• It helps in managing the state of an application in a predictable way.

• Redux follows a unidirectional data flow architecture.

• It uses actions, reducers, and a store to manage the state of an application.

• Redux is commonly used with React to build scalable and maintainable applications.

Call, Apply, and Bind are methods in JavaScript used to manipulate the value of 'this' in a function.

• Call: Invokes a function with a specified 'this' value and arguments provided individually.

• Apply: Invokes a function with a specified 'this' value and arguments provided as an array.

• Bind: Creates a new function with a specified 'this' value and arguments provided as a list.

Higher order function takes a function as an argument or returns a function. Higher order component is a function that takes a component and returns a new component.

• Higher order function is a function that operates on other functions, either by taking them as arguments or by returning them.

• Higher order component is a function that takes a component and returns a new component with additional functionality.

• Higher order functions and components are used to create reusable code ...read more

Meta tags are HTML tags that provide metadata about a webpage. Position refers to the placement of an element on a webpage. Promise is a JavaScript object representing the eventual completion or failure of an asynchronous operation. Callback is a function passed as an argument to another function to be executed after a specific event occurs. Pseudo elements and pseudo classes are CSS selectors that allow styling of specific parts of an element.

• Meta tags provide metadata about...read more

Angular offers two-way data binding, dependency injection, and a robust ecosystem of tools and libraries.

• Two-way data binding allows for automatic synchronization of data between the model and the view, reducing the need for manual DOM manipulation.

• Dependency injection simplifies the process of managing dependencies and promotes code reusability.

• Angular has a large ecosystem of tools and libraries, such as Angular Material for UI components and Angular CLI for project scaffol...read more

Functional components are stateless and use functional programming concepts, while class-based components are stateful and use object-oriented programming concepts.

• Functional components are simpler and easier to read and test.

• Class-based components have access to lifecycle methods and state.

• Functional components are preferred for simple UI components, while class-based components are preferred for complex UI components.

• Functional components can be written as arrow functions, ...read more

React is a JavaScript library for building user interfaces.

• React allows for building reusable UI components.

• It uses a virtual DOM for efficient rendering.

• React can be used for both web and mobile app development.

• It supports server-side rendering for improved SEO.

• React is maintained by Facebook and has a large community of developers.

The figure tag is used to group images and their captions together, while the img tag is used to display a single image.

• Figure tag is used to group images and their captions together.

• Img tag is used to display a single image.

• Figure tag can contain multiple images and text, while img tag is standalone.

• Figure tag is often used for image galleries or diagrams.

• Img tag is used for displaying a single image on a webpage.

To render a list in React, use map() function to iterate over an array of data and return a list of components. State is mutable data managed within a component, while props are immutable data passed from parent to child components.

• To render a list in React, use map() function to iterate over an array of data and return a list of components.

• Example: const items = ['item1', 'item2', 'item3']; items.map(item =>

• {item}
)

• State is mutable data managed within a component and can be ...read more

Webpage optimization techniques include minifying CSS and JS files, optimizing images, using asynchronous loading for scripts, and reducing render-blocking scripts.

• Minify CSS and JS files to reduce file sizes and improve loading times.

• Optimize images by compressing them and using the correct file format (e.g. JPEG for photographs, PNG for graphics).

• Use asynchronous loading for scripts to prevent them from blocking the rendering of the page.

• Reduce render-blocking scripts by mo...read more

React is a JavaScript library for building user interfaces. It is different from Angular and Vue in terms of architecture, data binding, and learning curve.

• React is a library, while Angular and Vue are frameworks.

• React uses a virtual DOM for better performance, while Angular and Vue use a real DOM.

• React follows a unidirectional data flow, while Angular and Vue use bidirectional data binding.

• React has a smaller learning curve compared to Angular, which has a steeper learning c...read more

Creating a dynamic table with object key pair mapping.

• Create a table element in HTML

• Loop through the object and create table rows and cells dynamically

• Use object keys to map to table headers and values to map to table cells

React has two types of hook methods: State Hooks and Effect Hooks.

• State Hooks manage state in functional components.

• Effect Hooks manage side effects in functional components.

• useState() is an example of State Hook.

• useEffect() is an example of Effect Hook.

Prototype in JS refers to the mechanism by which objects in JavaScript inherit properties and methods from other objects.

• Prototype chain allows objects to inherit properties and methods from other objects

• Prototype-based inheritance is a key feature of JavaScript

• Example: Creating a new object using a constructor function and adding methods to its prototype

Good UX is intuitive and satisfying, while bad UX is confusing and frustrating for users.

• Intuitiveness: Good UX allows users to navigate easily without confusion. For example, a well-structured menu helps users find information quickly.

• Consistency: Good UX maintains consistent design elements (colors, fonts) across the platform. For instance, using the same button style throughout an app.

• Feedback: Good UX provides clear feedback for user actions. For example, a loading spinne...read more

Yes, I have experience writing tests in React using Jest.

• I have experience writing unit tests for React components using Jest.

• I am familiar with testing libraries like Enzyme for React component testing.

• I understand how to write snapshot tests to ensure UI consistency in React applications.

Performance issues in Angular can be handled by optimizing code, reducing HTTP requests, and using lazy loading.

• Optimize code by using trackBy in ngFor loops

• Reduce HTTP requests by using caching and pagination

• Use lazy loading to load only necessary components

• Use AOT compilation to reduce load time

• Avoid using ngIf with heavy computations

• Use ChangeDetectionStrategy.OnPush to reduce change detection cycles

Sass is a preprocessor scripting language that is interpreted or compiled into Cascading Style Sheets (CSS).

• Sass allows for variables, nesting, and mixins, making CSS code more maintainable and DRY.

• It provides features like inheritance, functions, and loops, which help in writing cleaner and more organized stylesheets.

• Sass also supports modular and reusable code, improving development efficiency and scalability.

• By using Sass, developers can easily manage large and complex sty...read more

Props drilling is passing props through multiple levels of components. Higher order component is a function that takes a component and returns a new component.

• Props drilling involves passing props from a parent component to a deeply nested child component, which can lead to prop pollution and make the code harder to maintain.

• Higher order component is a pattern where a function takes a component and returns a new component with additional props or functionality.

• Example of prop...read more

webCompliance rules are guidelines that ensure websites meet legal and regulatory requirements. webForm 2.0 is a web development framework.

• webCompliance rules are used to ensure websites adhere to accessibility, privacy, and security standards.

• These rules help websites avoid legal issues and provide a better user experience.

• Examples of webCompliance rules include WCAG (Web Content Accessibility Guidelines) for accessibility and GDPR (General Data Protection Regulation) for pr...read more

In jQuery, you can add a class name to an element using the addClass() method.

• Use the addClass() method in jQuery to add a class name to an element.

• Syntax: $(selector).addClass(className);

• Example: $('button').addClass('active');

Use the 'srcset' attribute in the 'img' tag to make images responsive without using CSS or Bootstrap.

• Use the 'srcset' attribute in the 'img' tag to provide multiple image sources with different resolutions.

• Specify the 'sizes' attribute to define the layout breakpoints for different screen sizes.

• Include the 'width' attribute to help the browser determine the correct image size to display.

• Example: <img src='small.jpg' srcset='medium.jpg 1000w, large.jpg 2000w' sizes='(max-width...read more

A breadcrumb is a navigation element that shows the user's current location within a website or application.

• A breadcrumb typically appears horizontally at the top of a page or below the navigation bar.

• It consists of a series of links, with each link representing a higher-level page or section.

• The last link in the breadcrumb represents the current page or section and is often not clickable.

• Breadcrumb navigation helps users understand their location within a website and provide...read more

Div is a block-level element for layout, while span is an inline element for styling text.

• Div is used for grouping larger sections of content, e.g., <div class='container'>...</div>

• Span is used for styling small portions of text, e.g., <span class='highlight'>text</span>

• Div elements take up the full width available, while span elements only take up as much width as their content.

• Div can contain other block elements, while span is typically used within block elements.

Use SCSS to apply background color to nested li elements and utilize mixins.

• Use nesting to target the li elements within a parent element

• Apply background color to the 2nd li element using the :nth-child() selector

• Define and use mixins to reuse styles across the codebase

The string can be reversed in one line using the split(), reverse(), and join() methods.

• Use the split() method to convert the string into an array of characters

• Use the reverse() method to reverse the order of the array elements

• Use the join() method to convert the reversed array back into a string