100+ 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.

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

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.

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.

Lazy loading is a technique to defer loading of non-critical resources until they are needed.

• Lazy loading improves page load time and performance.

• It is commonly used for images, videos, and other media files.

• Lazy loading can be implemented using JavaScript libraries like LazyLoad or by using the Intersection Observer API.

• Lazy loading can also be implemented in frameworks like Angular and React.

The figure tag is used to group media content with a caption, while the img tag is used to display an image.

• The figure tag is used to group media content, such as images, videos, or illustrations, with a caption.

• The img tag is used specifically to display an image on a web page.

• The figure tag can contain multiple media elements, while the img tag is used for a single image.

• The figure tag provides semantic meaning and accessibility for media content.

• The img tag is a self-closi...read more

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

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

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.

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

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

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

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

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');

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

Use HTML's 'img' tag and set the 'width' attribute to '100%'.

• Use 'img' tag with 'src' attribute to specify the image source.

• Set the 'width' attribute to '100%' to make it responsive.

• Optionally, use 'height' attribute to maintain aspect ratio.

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

Redux is a predictable state container for JavaScript apps. It helps manage the state of an application in a single immutable state tree.

• Redux stores the entire state of an application in a single immutable state tree.

• The state tree is read-only, and changes are made by dispatching actions.

• Reducers specify how the state changes in response to actions.

• The store holds the state tree, allows access to state via getState(), and allows state to be updated via dispatch(action).

• Midd...read more

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

The __proto__ is a property that points to the prototype of an object, while prototype is a property of a constructor function.

• The __proto__ property is used to access the prototype of an object.

• The prototype property is used to add properties and methods to a constructor function.

• The __proto__ property is deprecated and should not be used in production code.

• Changes to the prototype of a constructor function will affect all instances of that constructor function.

UI Developer interview questions covering topics like rm vs em, MapObject vs Object, BOM, function currying, Pure component, and virtual dom.

• rm vs em: rm is relative to the font size of the root element, while em is relative to the font size of the element itself.

• MapObject vs Object: MapObject is a method that creates a new array with the results of calling a provided function on every element in the array, while Object is a global object that represents the properties of Jav...read more

I manage state using React's useState hook and context API for global state management.

• Using React's useState hook to manage local component state

• Utilizing React's context API for global state management

• Implementing Redux for complex state management scenarios

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

Closures in JavaScript are functions that have access to variables from their outer scope even after the outer function has finished executing.

• Closures allow functions to access variables from their parent function's scope

• They are created whenever a function is defined within another function

• Closures can be used to create private variables and functions

HTML5 is the latest version of HTML used to structure content on the web. CSS3 is the latest version of CSS used to style web pages. Media queries are used to apply different styles based on the device screen size.

• HTML5 provides new semantic elements like

  ,

• CSS3 provides new features like border-radius, box-shadow, etc.

• Media queries are written using @media rule and can be used to apply different styles for different screen sizes.

• Example of media query: @media screen ...read more

React is a JavaScript library for building user interfaces.

• React is a popular JavaScript library for building user interfaces.

• To create a tab structure in React, you can use components like Tabs and TabPanels.

• When a tab is clicked, you can use state to show or hide the content of that tab.

Angular is a JavaScript framework for building web applications. JavaScript is a programming language used for creating interactive web pages. Hosting refers to the process of making a website accessible on the internet. A closure is a function that has access to variables in its outer scope.

• Angular is a front-end framework used for building dynamic web applications.

• JavaScript is a programming language that allows developers to create interactive web pages and web application...read more

To fix cumulative layout shift issues, ensure all images and media have dimensions specified in HTML, use CSS aspect ratio boxes, and prioritize loading critical resources.

• Specify dimensions for all images and media in HTML to prevent layout shifts.

• Use CSS aspect ratio boxes to reserve space for images before they load.

• Prioritize loading critical resources to avoid sudden layout changes.

The question is unclear and lacks context.

• Please provide more information about the bus booking system.

• What is the purpose of the inventory and schedules?

• How does the buspar integrate with Google Maps?

• What specific tasks would a UI Developer be responsible for in this project?

display: None removes the element from the flow of the document, while visibility: 0 hides the element but still takes up space.

• display: None removes the element from the document flow, making it invisible and not taking up any space.

• visibility: 0 hides the element visually, but it still occupies space in the layout.

• display: None is commonly used to hide elements completely, while visibility: 0 is used to hide elements while preserving the layout.

React uses virtual DOM and efficient rendering techniques to make it faster than other frameworks.

• React uses virtual DOM which reduces the number of direct DOM manipulations, making it faster.

• React uses efficient rendering techniques like shouldComponentUpdate and PureComponent to optimize rendering.

• React also has a one-way data flow which makes it easier to manage and update data, improving performance.

• React's modular architecture allows for code reuse and reduces redundancy...read more

Redux is a predictable state container for JavaScript apps. It helps manage the state of an application in a centralized manner.

• Redux is used for state management in JavaScript applications.

• It provides a predictable state container, making it easier to manage and update the state of an application.

• Redux follows a unidirectional data flow, where the state is updated through actions and reducers.

• It allows for better separation of concerns by keeping the state separate from the ...read more

Use the delay() method in jQuery to add delay for animation.

• Use the delay() method before the animation function.

• Specify the duration of the delay in milliseconds as an argument.

• Example: $(element).delay(1000).fadeOut();

Fetching and selecting country, state, and city data from API using React

• Use axios or fetch to get data from API

• Create dropdown menus for country, state, and city selection

• Use onChange event to update state based on user selection

• Filter data based on selected country and state to display relevant cities

Authentication verifies a user's identity, while authorization determines what a user can access.

• Authentication confirms a user's identity through credentials like username and password.

• Authorization controls access to resources based on the authenticated user's permissions.

• Example: Logging into a website (authentication) and then being able to view/edit specific pages based on your role (authorization).

A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward.

• Convert the given string to lowercase and remove any non-alphanumeric characters

• Reverse the string and compare it with the original string to check for palindrome

• Examples: 'racecar' is a palindrome, 'hello' is not a palindrome

Ajax is a technique used to update parts of a web page without reloading the entire page.

• Ajax stands for Asynchronous JavaScript and XML.

• It allows for asynchronous communication between the client and server.

• Ajax uses XMLHttpRequest object to send and receive data from the server.

• It can update the content of a web page dynamically without refreshing the whole page.

• Ajax is commonly used for creating interactive web applications.

Code to find unique element from an array

• Loop through array and compare each element with rest of the array

• If element is not repeated, add it to a new array

• Return the new array with unique elements

Custom directives in AngularJS allow you to create reusable components.

• Create a new directive using the directive() method

• Specify the directive's behavior using the link() method

• Use the directive in HTML using its name as an attribute

• Pass data to the directive using attributes

• Example:

Angular lifecycle hooks are methods that allow you to tap into specific points in a component's lifecycle.

• ngOnChanges: Called when an input property changes

• ngOnInit: Called once the component is initialized

• ngDoCheck: Called during every change detection run

• ngAfterContentInit: Called after content (ng-content) has been projected into the component

• ngAfterContentChecked: Called after every check of the projected content

• ngAfterViewInit: Called after the component's view has been ...read more

Prototypal Inheritance in JavaScript is a way of creating objects based on existing objects.

• In JavaScript, each object has a prototype property which allows one object to inherit properties and methods from another object.

• When a property or method is accessed on an object, JavaScript will first look for it on the object itself, then on its prototype, and so on up the prototype chain.

• Prototypal Inheritance allows for code reusability and helps in creating a hierarchy of object...read more

Sorting an array without using built-in JS methods

• Create a custom sorting function using a sorting algorithm like bubble sort, selection sort, or insertion sort

• Compare each element in the array and swap them if they are in the wrong order

• Repeat the process until the array is fully sorted