N+A React Js Frontend Developer Interview Questions and Answers

Q1. What is the JavaScript code for finding repeating alphabets?
Ans. 
Use JavaScript to find repeating alphabets in an array of strings.
• Loop through each string in the array

• For each string, loop through each character and check if it is repeated

• Store the repeating alphabets in a separate array
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Q2. What are the Angular lifecycle hooks?
Ans. 
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

• ng...read more
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Codility consists of two Angular questions: the first involves creating a form, while the second pertains to developing a searchable input field, along with one DSA coding question.

Q1. How do you build form validations in angular
Ans. 
Form validations in Angular are built using Angular forms and validators.
• Use Angular forms to create form controls and group them together

• Apply built-in validators like required, minlength, maxlength, pattern, etc.

• Create custom validators for complex validation requirements

• Display error messages based on validation status

• Use reactive forms for more control and flexibility
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Q2. How will you create reusable loading logic in angular
Ans. 
Create a service with a loading state and methods to show/hide loading indicators
• Create a loading service with a boolean property 'isLoading'

• Add methods in the service to set isLoading to true/false

• Inject the loading service in components where loading indicators are needed
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Q3. JS questions which includes closure and promise.race
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Hacker rank test was sent which consisted of react, js, HTML, css, j query and Java questions. You’ve to complete the test in 60 mins

Q1. Promise, closure, diff btw let and const
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Q2. Define virtual dom, viewport, redux, use effect hook
Ans. 
Virtual DOM is a lightweight copy of the actual DOM, viewport is the visible area of a web page, Redux is a state management tool, useEffect hook is used for side effects in React components.
• Virtual DOM is a lightweight copy of the actual DOM, used for efficient updates.

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

• Redux is a state management tool for managing application state in a predictable way.

• us...read more
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Q1. What are the hooks you used?
Ans. 
I have used useState, useEffect, useContext, and useRef hooks in my projects.
• useState - for managing state in functional components

• useEffect - for handling side effects in functional components

• useContext - for accessing context in functional components

• useRef - for accessing DOM elements or storing mutable values
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Q2. Complete details of last project worked
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Q1. React hooks - custom hooks, hooks rules, useEffect vs useLayoutEffect, useReducer Lifecycle with useEffect Context - When, how and why to use it? React 18 new features
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Q2. What does strict mode do? Accessibility in react How forwardRef works? Keys in react controlled components, uncontrolled components, how to use those?
Ans. 
Explaining the features and usage of ReactJS
• Strict mode catches common mistakes and enforces best practices

• ForwardRef allows passing refs to child components

• Keys help React identify which items have changed, added, or removed

• Controlled components are stateful and rely on props to update, while uncontrolled components manage their own state

• Accessibility in React involves using ARIA attributes and semantic HTML
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Q3. ES6 features Shallow cloning and deep cloning How to deep clone nested objects? Hoisting JS execution cycle - call stack, event loop and callbacks
Ans. 
ES6 features, shallow and deep cloning, hoisting, JS execution cycle.
• ES6 features include arrow functions, template literals, let and const, destructuring, spread and rest operators, etc.

• Shallow cloning creates a new object with the same properties as the original object. Deep cloning creates a new object with all nested objects also cloned.

• To deep clone nested objects, use a recursive function or a library like lodash...read more
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Q4. Tell us about a challenging recently faced by you
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Q5. React testing How to test hooks?
Ans. 
Hooks can be tested using React Testing Library or Enzyme.
• Use React Testing Library's renderHook() method to test hooks

• Test the hook's return value and its behavior on re-renders

• Use Enzyme's shallow() or mount() methods to test hooks

• Mock any external dependencies used in the hook

• Test edge cases and error handling
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Round duration - 120 minutes
Round difficulty - Easy

Round duration - 120 minutes
Round difficulty - Easy

Q1. What is the difference between TRUNCATE and DELETE in a database management system?
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Round duration - 30 minutes
Round difficulty - Easy

Q1. 
Triplets with Given Sum Problem
Given an array or list ARR consisting of N integers, your task is to identify all distinct triplets within the array that sum up to a specified number K.
Explanation:
A t...read more
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Round duration - 5 minutes
Round difficulty - Easy