Top JavaScript Interview Questions and Expert Answers with Code Examples
Flatten a Nested Object
Question : Write a function to flatten a nested JavaScript object.
Code :
function flattenObject(obj, prefix = '', res = {}) {
** for (let key in obj) {**
** const newKey = prefix ? ${prefix}.${key} : key;**
** if (typeof obj[key] === 'object' && obj[key] !== null) {**
** flattenObject(obj[key], newKey, res);**
** } else {**
** res[newKey] = obj[key];**
** }**
** }**
** return res;**
}
console.log(flattenObject({ a: { b: { c: 1 } }, d: 2 }));
// Output: { 'a.b.c': 1, d: 2 }
2. Find Duplicates in an Array
Question : Write a function to find duplicate values in an array.
Code :
function findDuplicates(arr) {
** const counts = {};**
** return arr.filter(item => counts[item] ? true : (counts[item] = 1, false));**
}
console.log(findDuplicates([1, 2, 2, 3, 4, 4, 5]));
// Output: [2, 4]
3. Implement debounce
Question : Write a debounce function that limits the rate a function is called.
Code :
function debounce(func, delay) {
** let timer;**
** return function (...args) {**
** clearTimeout(timer);**
** timer = setTimeout(() => func.apply(this, args), delay);**
** };**
}
const log = debounce(() => console.log('Logged after 1s'), 1000);
log();
4. Reverse a String Recursively
Question : Write a recursive function to reverse a string.
Code :
function reverseString(str) {
** if (str === "") return "";**
** return reverseString(str.slice(1)) + str[0];**
}
console.log(reverseString("hello"));
// Output: "olleh"
5. Check for Palindrome
Question : Write a function to check if a string is a palindrome.
Code :
function isPalindrome(str) {
** const cleaned = str.toLowerCase().replace(/[^a-z]/g, '');**
** return cleaned === cleaned.split('').reverse().join('');**
}
console.log(isPalindrome("A man, a plan, a canal, Panama"));
// Output: true
Read more... ?
JavaScript interview questions & answers with code
JavaScript interview questions & answers with code
React interviews questions and answers with code
React interviews questions and answers with code
Angular interview questions
Angular interview questions
CSS Interview Questions
CSS Interview Questions along with their answers and Code
The above is the detailed content of JavaScript interview questions & answers with code. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
Java vs. JavaScript: Clearing Up the Confusion
Jun 20, 2025 am 12:27 AM
Java and JavaScript are different programming languages, each suitable for different application scenarios. Java is used for large enterprise and mobile application development, while JavaScript is mainly used for web page development.
Mastering JavaScript Comments: A Comprehensive Guide
Jun 14, 2025 am 12:11 AM
CommentsarecrucialinJavaScriptformaintainingclarityandfosteringcollaboration.1)Theyhelpindebugging,onboarding,andunderstandingcodeevolution.2)Usesingle-linecommentsforquickexplanationsandmulti-linecommentsfordetaileddescriptions.3)Bestpracticesinclud
Javascript Comments: short explanation
Jun 19, 2025 am 12:40 AM
JavaScriptcommentsareessentialformaintaining,reading,andguidingcodeexecution.1)Single-linecommentsareusedforquickexplanations.2)Multi-linecommentsexplaincomplexlogicorprovidedetaileddocumentation.3)Inlinecommentsclarifyspecificpartsofcode.Bestpractic
How to work with dates and times in js?
Jul 01, 2025 am 01:27 AM
The following points should be noted when processing dates and time in JavaScript: 1. There are many ways to create Date objects. It is recommended to use ISO format strings to ensure compatibility; 2. Get and set time information can be obtained and set methods, and note that the month starts from 0; 3. Manually formatting dates requires strings, and third-party libraries can also be used; 4. It is recommended to use libraries that support time zones, such as Luxon. Mastering these key points can effectively avoid common mistakes.
JavaScript vs. Java: A Comprehensive Comparison for Developers
Jun 20, 2025 am 12:21 AM
JavaScriptispreferredforwebdevelopment,whileJavaisbetterforlarge-scalebackendsystemsandAndroidapps.1)JavaScriptexcelsincreatinginteractivewebexperienceswithitsdynamicnatureandDOMmanipulation.2)Javaoffersstrongtypingandobject-orientedfeatures,idealfor
Why should you place tags at the bottom of the ?
Jul 02, 2025 am 01:22 AM
PlacingtagsatthebottomofablogpostorwebpageservespracticalpurposesforSEO,userexperience,anddesign.1.IthelpswithSEObyallowingsearchenginestoaccesskeyword-relevanttagswithoutclutteringthemaincontent.2.Itimprovesuserexperiencebykeepingthefocusonthearticl
JavaScript: Exploring Data Types for Efficient Coding
Jun 20, 2025 am 12:46 AM
JavaScripthassevenfundamentaldatatypes:number,string,boolean,undefined,null,object,andsymbol.1)Numbersuseadouble-precisionformat,usefulforwidevaluerangesbutbecautiouswithfloating-pointarithmetic.2)Stringsareimmutable,useefficientconcatenationmethodsf
What's the Difference Between Java and JavaScript?
Jun 17, 2025 am 09:17 AM
Java and JavaScript are different programming languages. 1.Java is a statically typed and compiled language, suitable for enterprise applications and large systems. 2. JavaScript is a dynamic type and interpreted language, mainly used for web interaction and front-end development.
