10+ NeoSOFT React Js Frontend Developer Interview Questions and Answers

Authentication verifies the identity of a user, while authorization determines the user's access rights.

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

• Authorization determines what actions the authenticated user is allowed to perform.

• Authentication precedes authorization in the security process.

• Example: Logging into a website (authentication) and then accessing specific pages based on user roles (authorization).

Local storage persists even after the browser is closed, while session storage is cleared when the browser is closed.

• Local storage has no expiration date, while session storage expires when the browser is closed.

• Local storage stores data with no limit, while session storage has a limit of around 5MB.

• Local storage data is available across all windows/tabs for that domain, while session storage data is only available within the same tab.

• Example: Local storage can be used for st...read more

Semantic tags in HTML are specific tags that provide meaning to the content they enclose.

• Semantic tags help search engines and screen readers understand the structure of a webpage.

• Examples of semantic tags include <header>, <footer>, <nav>, <article>, <section>, <aside>, <main>, <figure>, <figcaption>.

• Using semantic tags improves SEO and accessibility of a website.

Map is used to transform each element of an array, while Filter is used to select elements based on a condition.

• Map returns a new array with the same length as the original array, but with each element transformed based on a provided function.

• Filter returns a new array with only the elements that pass a provided condition function.

• Example for Map: [1, 2, 3].map(num => num * 2) will result in [2, 4, 6].

• Example for Filter: [1, 2, 3, 4, 5].filter(num => num % 2 === 0) will resul...read more

Map creates a new array with the results of calling a provided function on every element, while forEach executes a provided function once for each array element.

• Map returns a new array with the same length as the original array, while forEach does not return anything.

• Map does not mutate the original array, while forEach can mutate the original array.

• Map is more suitable for transforming data and creating a new array, while forEach is used for executing a function on each elem...read more

ES6 is the latest version of ECMAScript with new features like arrow functions, classes, and template literals.

• Arrow functions provide a more concise syntax for writing functions.

• Classes allow for easier object-oriented programming in JavaScript.

• Template literals make it easier to work with strings by allowing interpolation and multiline strings.

Currying is a technique in functional programming where a function with multiple arguments is transformed into a sequence of nested functions, each taking a single argument.

• Currying helps in creating reusable functions and partial application.

• It allows you to create new functions by fixing some parameters of an existing function.

• Example: const add = (a) => (b) => a + b; add(2)(3) will return 5.

useMemo is used for memoizing values, while useCallback is used for memoizing functions.

• useMemo is used to memoize a value and only recompute it when its dependencies change.

• useCallback is used to memoize a function instance and only re-create it when its dependencies change.

• Example: useMemo can be used to memoize the result of a complex computation, while useCallback can be used to memoize a callback function passed to a child component.

Semantic tags are HTML tags that clearly define the content they contain for better accessibility and SEO.

• Semantic tags provide meaning to the content they enclose, making it easier for search engines to understand the structure of the page.

• Examples of semantic tags include

  ,

• Using semantic tags improves the accessibility of the website for users with disabilities, as screen readers can interpret the content more accurately.

Promise chaining is a technique in JavaScript where multiple asynchronous operations are chained together to execute sequentially.

• Allows for handling multiple asynchronous operations in a more readable and organized way

• Each promise in the chain returns a new promise, allowing for further chaining

• Helps avoid callback hell by nesting promises inside each other

• Example: promise1.then(result => { return promise2; }).then(result => { return promise3; })

Redux is a predictable state container for JavaScript apps.

• Redux is a state management tool commonly used with React to manage the application's state in a predictable way.

• It helps in maintaining a single source of truth for the state of the entire application.

• Redux follows a unidirectional data flow, making it easier to understand how data changes over time.

• Actions are dispatched to update the state in Redux, and reducers specify how the state should change in response to th...read more

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

• Hooks were introduced in React 16.8.

• They allow you to use state and other React features in functional components.

• Some commonly used hooks are useState, useEffect, useContext, and useReducer.

Progressive web apps are web applications that provide a native app-like experience to users, with features like offline access and push notifications.

• Progressive web apps use modern web capabilities to provide a user experience similar to native apps.

• They are reliable, load quickly, and work offline.

• They can be installed on the user's device and send push notifications.

• Examples include Twitter Lite, Flipkart Lite, and Starbucks.

Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope during compilation.

• Variable declarations are hoisted but not their initializations.

• Function declarations are fully hoisted, meaning they can be called before they are declared.

• Hoisting can lead to unexpected behavior if not understood properly.

Virtual DOM is a lightweight copy of the actual DOM that React uses to improve performance by minimizing direct manipulation of the actual DOM.

• Virtual DOM is a concept in React where a lightweight copy of the actual DOM is created and updated in memory.

• When changes are made to the virtual DOM, React compares it with the actual DOM and only updates the necessary parts, reducing the number of direct manipulations to the actual DOM.

• This process helps improve performance by minim...read more

CSS positions include static, relative, absolute, fixed, and sticky.

• Static - default position, elements are positioned according to the normal flow of the document

• Relative - positioned relative to its normal position

• Absolute - positioned relative to the nearest positioned ancestor

• Fixed - positioned relative to the viewport

• Sticky - acts like a combination of relative and fixed positioning

Synthetic events in React are events that are normalized by React to ensure consistent behavior across different browsers.

• Synthetic events are instances of the SyntheticEvent object in React.

• They are cross-browser compatible and have the same interface as native events.

• They are used to handle events like onClick, onChange, etc. in React components.

• Example: Click me