30+ Junior Frontend Developer Interview Questions and Answers

This function counts down from a given time in seconds to zero, logging each second to the console.

• Use a loop to iterate from the given time down to 0.

• Utilize setInterval to create a delay between each console.log.

• Ensure to clear the interval once the countdown reaches zero.

• Example: For an input of 5, the output will be 5, 4, 3, 2, 1, 0.

Flux is a state management pattern for building user interfaces, often used with React to manage data flow.

• Flux promotes unidirectional data flow, making it easier to understand how data changes in an application.

• It consists of four main components: Actions, Dispatcher, Stores, and Views.

• Actions are payloads of information that send data from the application to the dispatcher.

• The Dispatcher is a central hub that manages all data flow in the application.

• Stores hold the applica...read more

I have used libraries like React, Redux, Axios, and Moment.js for frontend development.

• React

• Redux

• Axios

• Moment.js

Yes, Redux does not have built-in persistence for state.

• Redux itself does not have built-in persistence for state

• Persisting state in Redux typically involves using middleware like redux-persist or saving state to local storage

• Examples of persisting state in Redux include using redux-persist to save state to local storage or using cookies to store state

States in React are passed down from parent components to child components using props.

• States are passed down as props from parent components to child components

• Parent components can pass states to child components using props

• States can be updated in parent components and passed down to child components for re-rendering

Using useContext to implement increment and decrement feature in React

• Create a context using createContext()

• Define a provider component to wrap the components that need access to the context

• Use useContext() hook in the components to access the context and update the state

• Implement functions for increment and decrement within the context provider

I have used React versions 16 and 17 in my projects.

• Used React 16 for a project that required class components and lifecycle methods

• Currently using React 17 for a project that focuses on functional components and hooks

Yes, multiple stores can be created in Redux for managing different parts of the application state.

• Redux allows creating multiple stores, each with its own reducers and actions

• This can be useful for managing different parts of the application state separately

• Example: creating one store for user authentication and another for managing shopping cart

Redux passes states to components through the connect function provided by react-redux library.

• Redux passes states to components by connecting the component to the Redux store using the connect function.

• The connect function takes mapStateToProps as an argument, which maps the state from the Redux store to props of the component.

• The connected component can then access the state from the Redux store as props.

Browsers use various storage options like cookies, local storage, session storage, and IndexedDB.

• Cookies are small pieces of data stored in the browser that can be accessed by both the server and the client.

• Local storage allows storing data without expiration date, and it remains even after the browser is closed.

• Session storage is similar to local storage but data is cleared when the session ends.

• IndexedDB is a low-level API for client-side storage of significant amounts of s...read more

HTML structures content, CSS styles it, and JavaScript adds interactivity to web pages.

• HTML (HyperText Markup Language) is used to create the structure of web pages. Example: <h1>Title</h1>

• CSS (Cascading Style Sheets) is used for styling HTML elements. Example: body { background-color: blue; }

• JavaScript is a programming language that enables interactivity. Example: document.getElementById('myButton').onclick = function() { alert('Hello!'); };

useSelector and useDispatch hooks are used in React Redux for accessing state and dispatching actions respectively.

• useSelector hook is used to extract data from the Redux store state in a functional component.

• useDispatch hook is used to dispatch actions to the Redux store in a functional component.

• Example: const data = useSelector(state => state.data); dispatch(action());

HTML and CSS files are connected by linking the CSS file to the HTML file using the <link> tag in the <head> section of the HTML file.

• Use the <link> tag in the <head> section of the HTML file to link the CSS file.

• Specify the path to the CSS file in the href attribute of the <link> tag.

• Make sure the CSS file is saved with a .css extension.

• For example: <link rel='stylesheet' type='text/css' href='styles.css'>

Redux is a predictable state container for JavaScript apps.

• Single source of truth: The state of your whole application is stored in an object tree within a single store.

• State is read-only: The only way to change the state is to emit an action, an object describing what happened.

• Changes are made with pure functions: To specify how the state tree is transformed by actions, you write pure reducers.

• State changes are made with pure functions: To specify how the state tree is trans...read more

I regularly use HTML, CSS, and JavaScript in my work as a Junior Frontend Developer.

• HTML

• CSS

• JavaScript

Various programming languages are used in web development to create dynamic and interactive websites.

• HTML - used for creating the structure of web pages

• CSS - used for styling the appearance of web pages

• JavaScript - used for adding interactivity and dynamic elements to web pages

• PHP - used for server-side scripting and backend development

• Python - used for backend development and data processing

• Ruby - used for web development with the Ruby on Rails framework

• Java - used for build...read more

The critical rendering path is the sequence of steps browsers take to convert HTML, CSS, and JavaScript into pixels on the screen.

• Includes steps like parsing HTML, constructing the DOM tree, rendering the CSSOM, combining them into a render tree, layout, and painting.

• Optimizing the critical rendering path involves minimizing render-blocking resources, reducing the number of critical resources, and optimizing the order of resource loading.

• Examples of optimization techniques in...read more

useContext is used for accessing context values in functional components, while useReducer is used for managing state in a more complex way.

• useContext is used for accessing context values without prop drilling

• useReducer is used for managing state in a more complex way by using a reducer function

• useContext is simpler and more straightforward, while useReducer provides more control and flexibility

• Example: useContext can be used to access a theme context value in a component, wh...read more

Infinite scrolling is a design pattern that continuously loads content as the user scrolls down a webpage.

• Infinite scrolling helps to provide a seamless user experience by eliminating the need for pagination.

• It is commonly used in social media feeds, image galleries, and news websites.

• Infinite scrolling can be implemented using JavaScript to fetch and append new content dynamically.

TypeScript is used to add static typing to JavaScript, catching errors at compile time and improving code quality.

• Provides static typing, catching errors at compile time

• Improves code quality and maintainability

• Supports modern JavaScript features like ES6+

• Enhances code editor tooling and IntelliSense

• Facilitates easier refactoring and code navigation

Specificity in CSS determines which style rule is applied to an element when multiple rules have conflicting selectors.

• Specificity is calculated based on the type of selector used in a CSS rule.

• Inline styles have the highest specificity, followed by IDs, classes, and elements.

• Specificity is represented by a four-part value, with each part corresponding to a different type of selector.

• For example, the selector 'div p' has a lower specificity than 'p.class'.

Virtualization is the process of creating a virtual version of a device or resource, such as a server, storage device, network or operating system.

• Virtualization allows multiple virtual instances to run on a single physical machine, maximizing resource utilization.

• Examples of virtualization technologies include VMware, VirtualBox, and Docker.

• Virtualization can improve scalability, flexibility, and efficiency in IT environments.

I prioritize flexible layouts, media queries, and mobile-first design to ensure a seamless user experience across devices.

• Use fluid grids: Implement a grid system that uses percentages instead of fixed units (e.g., Bootstrap or CSS Grid).

• Media queries: Apply CSS rules based on device characteristics, such as screen width (e.g., @media screen and (max-width: 600px) {}).

• Mobile-first approach: Start designing for the smallest screens first and progressively enhance for larger de...read more

useContext is a React hook for managing global state within a component tree, while Redux is a standalone state management library for React applications.

• useContext is built into React and is used for managing local state within a component or passing data down through the component tree.

• Redux is a separate library that allows for managing global state across the entire application, with actions and reducers to update and access the state.

• useContext is simpler and more lightw...read more

The code will output 'undefined' and then '10' in the console.

• The variable 'a' is declared after the first console.log statement, so it will be undefined at that point.

• The value of 'a' is assigned as 10 before the second console.log statement, so it will output 10.

The CSS DOM (Document Object Model) is a representation of the structure of a webpage created by CSS styles.

• CSS DOM is a tree-like structure that represents the HTML elements of a webpage along with their CSS styles.

• It allows developers to access and manipulate the styles of HTML elements using CSS properties and selectors.

• Changes made to the CSS DOM dynamically update the visual appearance of the webpage.

• Example: Selecting an element with a specific class and changing its ba...read more

Debouncing and throttling are techniques used in web development to limit the number of times a function is called.

• Debouncing delays the execution of a function until after a specified time has elapsed without any further calls. It is typically used for events like scroll or resize that can fire multiple times in a short period.

• Throttling limits the rate at which a function is called. It ensures that the function is not called more than once in a specified time interval. It i...read more