JavaScript Interview Questions

 

1              What are the possible ways to create objects in JavaScript

2              What is prototype chain

3              What is the difference between Call, Apply and Bind

4              What is JSON and its common operations

5              What is the purpose of the array slice method

6              What is the purpose of the array splice method

7              What is the difference between slice and splice

8              How do you compare Object and Map

9              What is the difference between == and === operators

10           What are lambda or arrow functions

11           What is a first class function

12           What is a first order function

13           What is a higher order function

14           What is a unary function

15           What is the currying function

16           What is a pure function

17           What is the purpose of the let keyword

18           What is the difference between let and var

19           What is the reason to choose the name let as a keyword

20           How do you redeclare variables in switch block without an error

21           What is the Temporal Dead Zone

22           What is IIFE(Immediately Invoked Function Expression)

23           How do you decode or encode a URL in JavaScript?

24           What is memoization

25           What is Hoisting

26           What are classes in ES6

27           What are closures

28           What are modules

29           Why do you need modules

30           What is scope in javascript

31           What is a service worker

32           How do you manipulate DOM using a service worker

33           How do you reuse information across service worker restarts

34           What is IndexedDB

35           What is web storage

36           What is a post message

37           What is a cookie

38           Why do you need a Cookie

39           What are the options in a cookie

40           How do you delete a cookie

41           What are the differences between cookie, local storage and session storage

42           What is the main difference between localStorage and sessionStorage

43           How do you access web storage

44           What are the methods available on session storage

45           What is a storage event and its event handler

46           Why do you need web storage

47           How do you check web storage browser support

48           How do you check web workers browser support

49           Give an example of a web worker

50           What are the restrictions of web workers on DOM

51           What is a promise

52           Why do you need a promise

53           What are the three states of promise

54           What is a callback function

55           Why do we need callbacks

56           What is a callback hell

57           What are server-sent events

58           How do you receive server-sent event notifications

59           How do you check browser support for server-sent events

60           What are the events available for server sent events

61           What are the main rules of promise

62           What is callback in callback

63           What is promise chaining

64           What is promise.all

65           What is the purpose of the race method in promise

66           What is a strict mode in javascript

67           Why do you need strict mode

68           How do you declare strict mode

69           What is the purpose of double exclamation

70           What is the purpose of the delete operator

71           What is typeof operator

72           What is undefined property

73           What is null value

74           What is the difference between null and undefined

75           What is eval

76           What is the difference between window and document

77           How do you access history in javascript

78           How do you detect caps lock key turned on or not

79           What is isNaN

80           What are the differences between undeclared and undefined variables

81           What are global variables

82           What are the problems with global variables

83           What is NaN property

84           What is the purpose of isFinite function

85           What is an event flow

86           What is event bubbling

87           What is event capturing

88           How do you submit a form using JavaScript

89           How do you find operating system details

90           What is the difference between document load and DOMContentLoaded events

91           What is the difference between native, host and user objects

92           What are the tools or techniques used for debugging JavaScript code

93           What are the pros and cons of promises over callbacks

94           What is the difference between an attribute and a property

95           What is same-origin policy

96           What is the purpose of void 0

97           Is JavaScript a compiled or interpreted language

98           Is JavaScript a case-sensitive language

99           Is there any relation between Java and JavaScript

100         What are events

101         Who created javascript

102         What is the use of preventDefault method

103         What is the use of stopPropagation method

104         What are the steps involved in return false usage

105         What is BOM

106         What is the use of setTimeout

107         What is the use of setInterval

108         Why is JavaScript treated as Single threaded

109         What is an event delegation

110         What is ECMAScript

111         What is JSON

112         What are the syntax rules of JSON

113         What is the purpose JSON stringify

114         How do you parse JSON string

115         Why do you need JSON

116         What are PWAs

117         What is the purpose of clearTimeout method

118         What is the purpose of clearInterval method

119         How do you redirect new page in javascript

120         How do you check whether a string contains a substring

121         How do you validate an email in javascript

122         How do you get the current url with javascript

123         What are the various url properties of location object

124         How do get query string values in javascript

125         How do you check if a key exists in an object

126         How do you loop through or enumerate javascript object

127         How do you test for an empty object

128         What is an arguments object

129         How do you make first letter of the string in an uppercase

130         What are the pros and cons of for loop

131         How do you display the current date in javascript

132         How do you compare two date objects

133         How do you check if a string starts with another string

134         How do you trim a string in javascript

135         How do you add a key value pair in javascript

136         Is the '!--' notation represents a special operator

137         How do you assign default values to variables

138         How do you define multiline strings

139         What is an app shell model

140         Can we define properties for functions

141         What is the way to find the number of parameters expected by a function

142         What is a polyfill

143         What are break and continue statements

144         What are js labels

145         What are the benefits of keeping declarations at the top

146         What are the benefits of initializing variables

147         What are the recommendations to create new object

148         How do you define JSON arrays

149         How do you generate random integers

150         Can you write a random integers function to print integers with in a range

151         What is tree shaking

152         What is the need of tree shaking

153         Is it recommended to use eval

154         What is a Regular Expression

155         What are the string methods available in Regular expression

156         What are modifiers in regular expression

157         What are regular expression patterns

158         What is a RegExp object

159         How do you search a string for a pattern

160         What is the purpose of exec method

161         How do you change the style of a HTML element

162         What would be the result of 1+2+'3'

163         What is a debugger statement

164         What is the purpose of breakpoints in debugging

165         Can I use reserved words as identifiers

166         How do you detect a mobile browser

167         How do you detect a mobile browser without regexp

168         How do you get the image width and height using JS

169         How do you make synchronous HTTP request

170         How do you make asynchronous HTTP request

171         How do you convert date to another timezone in javascript

172         What are the properties used to get size of window

173         What is a conditional operator in javascript

174         Can you apply chaining on conditional operator

175         What are the ways to execute javascript after page load

176         What is the difference between proto and prototype

177         Give an example where do you really need semicolon

178         What is a freeze method

179         What is the purpose of freeze method

180         Why do I need to use freeze method

181         How do you detect a browser language preference

182         How to convert string to title case with javascript

183         How do you detect javascript disabled in the page

184         What are various operators supported by javascript

185         What is a rest parameter

186         What happens if you do not use rest parameter as a last argument

187         What are the bitwise operators available in javascript

188         What is a spread operator

189         How do you determine whether object is frozen or not

190         How do you determine two values same or not using object

191         What is the purpose of using object is method

192         How do you copy properties from one object to other

193         What are the applications of assign method

194         What is a proxy object

195         What is the purpose of seal method

196         What are the applications of seal method

197         What are the differences between freeze and seal methods

198         How do you determine if an object is sealed or not

199         How do you get enumerable key and value pairs

200         What is the main difference between Object.values and Object.entries method

201         How can you get the list of keys of any object

202         How do you create an object with prototype

203         What is a WeakSet

204         What are the differences between WeakSet and Set

205         List down the collection of methods available on WeakSet

206         What is a WeakMap

207         What are the differences between WeakMap and Map

208         List down the collection of methods available on WeakMap

209         What is the purpose of uneval

210         How do you encode an URL

211         How do you decode an URL

212         How do you print the contents of web page

213         What is the difference between uneval and eval

214         What is an anonymous function

215         What is the precedence order between local and global variables

216         What are javascript accessors

217         How do you define property on Object constructor

218         What is the difference between get and defineProperty

219         What are the advantages of Getters and Setters

220         Can I add getters and setters using defineProperty method

221         What is the purpose of switch-case

222         What are the conventions to be followed for the usage of switch case

223         What are primitive data types

224         What are the different ways to access object properties

225         What are the function parameter rules

226         What is an error object

227         When you get a syntax error

228         What are the different error names from error object

229         What are the various statements in error handling

230         What are the two types of loops in javascript

231         What is nodejs

232         What is an Intl object

233         How do you perform language specific date and time formatting

234         What is an Iterator

235         How does synchronous iteration works

236         What is an event loop

237         What is call stack

238         What is an event queue

239         What is a decorator

240         What are the properties of Intl object

241         What is an Unary operator

242         How do you sort elements in an array

243         What is the purpose of compareFunction while sorting arrays

244         How do you reversing an array

245         How do you find min and max value in an array

246         How do you find min and max values without Math functions

247         What is an empty statement and purpose of it

248         How do you get metadata of a module

249         What is a comma operator

250         What is the advantage of a comma operator

251         What is typescript

252         What are the differences between javascript and typescript

253         What are the advantages of typescript over javascript

254         What is an object initializer

255         What is a constructor method

256         What happens if you write constructor more than once in a class

257         How do you call the constructor of a parent class

258         How do you get the prototype of an object

259         What happens If I pass string type for getPrototype method

260         How do you set prototype of one object to another

261         How do you check whether an object can be extendable or not

262         How do you prevent an object to extend

263         What are the different ways to make an object non-extensible

264         How do you define multiple properties on an object

265         What is MEAN in javascript

266         What Is Obfuscation in javascript

267         Why do you need Obfuscation

268         What is Minification

269         What are the advantages of minification

270         What are the differences between Obfuscation and Encryption

271         What are the common tools used for minification

272         How do you perform form validation using javascript

273         How do you perform form validation without javascript

274         What are the DOM methods available for constraint validation

275         What are the available constraint validation DOM properties

276         What are the list of validity properties

277         Give an example usage of rangeOverflow property

278         Is enums feature available in javascript

279         What is an enum

280         How do you list all properties of an object

281         How do you get property descriptors of an object

282         What are the attributes provided by a property descriptor

283         How do you extend classes

284         How do I modify the url without reloading the page

285         How do you check whether an array includes a particular value or not

286         How do you compare scalar arrays

287         How to get the value from get parameters

288         How do you print numbers with commas as thousand separators

289         What is the difference between java and javascript

290         Does javascript supports namespace

291         How do you declare namespace

292         How do you invoke javascript code in an iframe from parent page

293         How do get the timezone offset from date

294         How do you load CSS and JS files dynamically

295         What are the different methods to find HTML elements in DOM

296         What is jQuery

297         What is V8 JavaScript engine

298         Why do we call javascript as dynamic language

299         What is a void operator

300         How to set the cursor to wait

301         How do you create an infinite loop

302         Why do you need to avoid with statement

303         What is the output of below for loops

304         List down some of the features of ES6

305         What is ES6

306         Can I redeclare let and const variables

307         Is const variable makes the value immutable

308         What are default parameters

309         What are template literals

310         How do you write multi-line strings in template literals

311         What are nesting templates

312         What are tagged templates

313         What are raw strings

314         What is destructuring assignment

315         What are default values in destructuring assignment

316         How do you swap variables in destructuring assignment

317         What are enhanced object literals

318         What are dynamic imports

319         What are the use cases for dynamic imports

320         What are typed arrays

321         What are the advantages of module loaders

322         What is collation

323         What is for...of statement

324         What is the output of below spread operator array

325         Is PostMessage secure

326         What are the problems with postmessage target origin as wildcard

327         How do you avoid receiving postMessages from attackers

328         Can I avoid using postMessages completely

329         Is postMessages synchronous

330         What paradigm is Javascript

331         What is the difference between internal and external javascript

332         Is JavaScript faster than server side script

333         How do you get the status of a checkbox

334         What is the purpose of double tilde operator

335         How do you convert character to ASCII code

336         What is ArrayBuffer

337         What is the output of below string expression

338         What is the purpose of Error object

339         What is the purpose of EvalError object

340         What are the list of cases error thrown from non-strict mode to strict mode

341         Do all objects have prototypes

342         What is the difference between a parameter and an argument

343         What is the purpose of some method in arrays

344         How do you combine two or more arrays

345         What is the difference between Shallow and Deep copy

346         How do you create specific number of copies of a string

347         How do you return all matching strings against a regular expression

348         How do you trim a string at the beginning or ending

349         What is the output of below console statement with unary operator

350         Does javascript uses mixins

351         What is a thunk function

352         What are asynchronous thunks

353         What is the output of below function calls

354         How to remove all line breaks from a string

355         What is the difference between reflow and repaint

356         What happens with negating an array

357         What happens if we add two arrays

358         What is the output of prepend additive operator on falsy values

359         How do you create self string using special characters

360         How do you remove falsy values from an array

361         How do you get unique values of an array

362         What is destructuring aliases

363         How do you map the array values without using map method

364         How do you empty an array

365         How do you rounding numbers to certain decimals

366         What is the easiest way to convert an array to an object

367         How do you create an array with some data

368         What are the placeholders from console object

369         Is it possible to add CSS to console messages

370         What is the purpose of dir method of console object

371         Is it possible to debug HTML elements in console

372         How do you display data in a tabular format using console object

373         How do you verify that an argument is a Number or not

374         How do you create copy to clipboard button

375         What is the shortcut to get timestamp

376         How do you flattening multi dimensional arrays

377         What is the easiest multi condition checking

378         How do you capture browser back button

379         How do you disable right click in the web page

380         What are wrapper objects

381         What is AJAX

382         What are the different ways to deal with Asynchronous Code

383         How to cancel a fetch request

384         What is web speech API

385         What is minimum timeout throttling

386         How do you implement zero timeout in modern browsers

387         What are tasks in event loop

388         What is microtask

389         What are different event loops

390         What is the purpose of queueMicrotask

391         How do you use javascript libraries in typescript file

392         What are the differences between promises and observables

393         What is heap

394         What is an event table

395         What is a microTask queue

396         What is the difference between shim and polyfill

397         How do you detect primitive or non primitive value type

398         What is babel

399         Is Node.js completely single threaded

400         What are the common use cases of observables

401         What is RxJS

402         What is the difference between Function constructor and function declaration

403         What is a Short circuit condition

404         What is the easiest way to resize an array

405         What is an observable

406         What is the difference between function and class declarations

407         What is an async function

408         How do you prevent promises swallowing errors

409         What is deno

410         How do you make an object iterable in javascript

411         What is a Proper Tail Call

412         How do you check an object is a promise or not

413         How to detect if a function is called as constructor

414         What are the differences between arguments object and rest parameter

415         What are the differences between spread operator and rest parameter

416         What are the different kinds of generators

417         What are the built-in iterables

418         What are the differences between for...of and for...in statements

419         How do you define instance and non-instance properties

420         What is the difference between isNaN and Number.isNaN?

421         How to invoke an IIFE without any extra brackets?

422         Is that possible to use expressions in switch cases?

423         What is the easiest way to ignore promise errors?

424         How do style the console output using CSS?

425         What is nullish coalescing operator (??)?

426         How do you group and nest console output?

427         What is the difference between dense and sparse arrays?

428         What are the different ways to create sparse arrays?

429         What is the difference between setTimeout, setImmediate and process.nextTick?

430         How do you reverse an array without modifying original array?

431         How do you create custom HTML element?

432         What is global execution context?

433         What is function execution context?

434         What is debouncing?

435         What is throttling?

436         What is optional chaining?