20+ Senior UI Developer Interview Questions and Answers

Questions related to React JS, optimization techniques, core web vitals, and webpack.

• React JS life cycle methods include componentDidMount, componentDidUpdate, and componentWillUnmount.

• Context API is used for sharing data between components without passing props down the component tree.

• Advantages of Context API include avoiding prop drilling and making it easier to manage global state.

• Disadvantages of Context API include potential performance issues and difficulty with testin...read more

Implementing setInterval using setTimeout and creating an Autocomplete feature in React.

• setInterval can be mimicked using setTimeout by recursively calling a function after a specified delay.

• Example: function myInterval(callback, delay) { setTimeout(() => { callback(); myInterval(callback, delay); }, delay); }

• For Autocomplete, maintain a state for user input and filter suggestions based on that input.

• Example: const filteredSuggestions = suggestions.filter(s => s.toLowerCase()...read more

Use 'for' attribute in label tag to associate with checkbox id

• Add 'for' attribute in label tag with value as the id of the checkbox input element

• Clicking on the label will toggle the checkbox state

No, media queries are necessary for responsive design.

• Media queries are used to apply different styles based on screen size

• Without media queries, the design would not adapt to different devices

• Responsive design is essential for a good user experience

Position relative and absolute are CSS properties used for positioning elements on a webpage.

• Position relative: element is positioned relative to its normal position in the document flow.

• Position absolute: element is positioned relative to its nearest positioned ancestor.

• Position absolute takes the element out of the normal document flow.

• Position relative can be used to create subtle adjustments to an element's position.

• Position absolute is often used for creating overlays or...read more

Event loop is a mechanism in JavaScript that handles asynchronous operations.

• JavaScript is a single-threaded language, meaning it can only execute one task at a time.

• Asynchronous programming allows multiple tasks to be executed simultaneously.

• Event loop is responsible for managing the execution of asynchronous code.

• Callbacks, Promises, and Async/Await are common ways to handle asynchronous code in JavaScript.

Meta tags in HTML are used to provide metadata about the HTML document.

• Meta tags are placed in the head section of an HTML document.

• They provide information such as character set, viewport settings, keywords, and description.

• Meta tags can also be used for search engine optimization (SEO) purposes.

• Example: <meta charset='UTF-8'>

Tags are used to define the structure of an element in HTML, while elements are the actual components that make up a webpage.

• Tags are enclosed in angle brackets (<>) and define the beginning and end of an element.

• Elements consist of the opening tag, content, and closing tag.

• Example: <p> is a tag that defines a paragraph element, while <p>This is a paragraph</p> is the complete paragraph element.

Mixin is a reusable block of code in SCSS that can be included in other stylesheets.

• Mixin allows developers to define a set of CSS declarations that can be reused throughout the stylesheet.

• It helps in reducing code duplication and makes the code more maintainable.

• Mixin can take arguments and can be used to generate different styles based on the arguments passed.

• Mixin can be defined using the @mixin directive and included using the @include directive.

Flexbox is one-dimensional layout while Grid is two-dimensional layout.

• Flexbox is best suited for arranging items in a single row or column.

• Grid is best suited for arranging items in rows and columns.

• Flexbox has a main axis and a cross axis.

• Grid has rows and columns that intersect to form grid cells.

• Flexbox is great for responsive design and centering items.

• Grid is great for complex layouts and aligning items precisely.

• Flexbox is supported by all modern browsers.

• Grid is suppo...read more

Viewport is the visible area of a web page displayed on a device's screen.

• Viewport determines how much content can be seen without scrolling

• It can be adjusted using meta tags in HTML or CSS media queries

• Viewport size varies depending on the device and orientation

• Viewport can affect the layout and responsiveness of a website

SCSS provides benefits like variables, nesting, mixins, and inheritance to make CSS more efficient and maintainable.

• SCSS allows for the use of variables, which can be reused throughout the stylesheet.

• Nesting in SCSS makes it easier to read and organize code.

• Mixins allow for the reuse of code snippets, reducing the amount of code needed.

• Inheritance in SCSS allows for the creation of base styles that can be extended and modified as needed.

• SCSS also provides functions and operat...read more

Reversing a string involves rearranging its characters in the opposite order, a common task in programming.

• Use built-in functions: In JavaScript, you can use str.split('').reverse().join('') to reverse a string.

• Iterate manually: Loop through the string from the end to the beginning and build a new string.

• Example in Python: ''.join(reversed('hello')) returns 'olleh'.

• Consider edge cases: An empty string or a single character should return the same string.

Box model is a fundamental concept in CSS that defines how elements are rendered on a web page.

• Box model consists of content, padding, border, and margin.

• Content is the actual content of the element.

• Padding is the space between the content and the border.

• Border is the line that surrounds the element.

• Margin is the space between the border and the adjacent elements.

• Box-sizing property can be used to change the box model behavior.

• Default box-sizing value is content-box.

• border-bo...read more

Context API is a feature in React that allows sharing data between components without having to pass props through every level of the component tree.

• Context API provides a way to pass data through the component tree without having to pass props down manually at every level.

• It is useful for sharing global data such as themes, user authentication, or language preferences.

• Context API consists of three main parts: Provider, Consumer, and useContext hook.

• Example: createContext() c...read more

Browser storages are used to store data locally on the user's browser.

• Browser storages include cookies, local storage, and session storage.

• Cookies are used to store small amounts of data that can be accessed by the server or client-side scripts.

• Local storage and session storage are used to store larger amounts of data that can only be accessed by client-side scripts.

• Browser storages can be used to improve user experience by storing user preferences and login information.

• Howev...read more

Hooks in React JS are functions that let you use state and other React features without writing a class.

• Hooks were introduced in React 16.8 to allow functional components to have state and lifecycle methods.

• useState() is a hook that allows you to add state to functional components.

• useEffect() is a hook that allows you to perform side effects in functional components.

• Custom hooks are reusable functions that can contain logic and stateful logic for components.

• Hooks provide a mo...read more