https://github.com/shubhamraj-24/javascript-interview-questions
List of all time 700+ javascipt interview questions , explaining each of them with proper examples.
https://github.com/shubhamraj-24/javascript-interview-questions
javascript javascript-interview javascript-interview-questions
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List of all time 700+ javascipt interview questions , explaining each of them with proper examples.
- Host: GitHub
- URL: https://github.com/shubhamraj-24/javascript-interview-questions
- Owner: shubhamraj-24
- Created: 2024-04-17T07:44:34.000Z (about 2 years ago)
- Default Branch: main
- Last Pushed: 2024-04-17T07:44:41.000Z (about 2 years ago)
- Last Synced: 2025-02-26T04:27:54.219Z (over 1 year ago)
- Topics: javascript, javascript-interview, javascript-interview-questions
- Language: JavaScript
- Homepage:
- Size: 573 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# JavaScript Interview Questions & Answers
> Click :star:if you like the project. Coding questions available [here](#coding-exercise).
---
### Table of Contents
| No. | Questions |
| --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 1 | [What are the possible ways to create objects in JavaScript](#what-are-the-possible-ways-to-create-objects-in-javascript) |
| 2 | [What is a prototype chain](#what-is-a-prototype-chain) |
| 3 | [What is the difference between Call, Apply and Bind](#what-is-the-difference-between-call-apply-and-bind) |
| 4 | [What is JSON and its common operations](#what-is-json-and-its-common-operations) |
| 5 | [What is the purpose of the array slice method](#what-is-the-purpose-of-the-array-slice-method) |
| 6 | [What is the purpose of the array splice method](#what-is-the-purpose-of-the-array-splice-method) |
| 7 | [What is the difference between slice and splice](#what-is-the-difference-between-slice-and-splice) |
| 8 | [How do you compare an Object with a Map](#how-do-you-compare-object-and-map) |
| 9 | [What is the difference between == and === operators](#what-is-the-difference-between--and--operators) |
| 10 | [What are lambda expression or arrow functions](#what-are-lambda-or-arrow-functions) |
| 11 | [What is a first class function](#what-is-a-first-class-function) |
| 12 | [What is a first order function](#what-is-a-first-order-function) |
| 13 | [What is a higher order function](#what-is-a-higher-order-function) |
| 14 | [What is a unary function](#what-is-a-unary-function) |
| 15 | [What is the currying function](#what-is-the-currying-function) |
| 16 | [What is a pure function](#what-is-a-pure-function) |
| 17 | [What is the purpose of the let keyword](#what-is-the-purpose-of-the-let-keyword) |
| 18 | [What is the difference between let and var](#what-is-the-difference-between-let-and-var) |
| 19 | [What is the reason to choose the name let as a keyword](#what-is-the-reason-to-choose-the-name-let-as-a-keyword) |
| 20 | [How do you redeclare variables in switch block without an error](#how-do-you-redeclare-variables-in-switch-block-without-an-error) |
| 21 | [What is the Temporal Dead Zone](#what-is-the-temporal-dead-zone) |
| 22 | [What is IIFE(Immediately Invoked Function Expression)](#what-is-iifeimmediately-invoked-function-expression) |
| 23 | [How do you decode or encode a URL in JavaScript?](#how-do-you-decode-or-encode-a-url-in-javascript) |
| 24 | [What is memoization](#what-is-memoization) |
| 25 | [What is Hoisting](#what-is-hoisting) |
| 26 | [What are classes in ES6](#what-are-classes-in-es6) |
| 27 | [What are closures](#what-are-closures) |
| 28 | [What are modules](#what-are-modules) |
| 29 | [Why do you need modules](#why-do-you-need-modules) |
| 30 | [What is scope in javascript](#what-is-scope-in-javascript) |
| 31 | [What is a service worker](#what-is-a-service-worker) |
| 32 | [How do you manipulate DOM using a service worker](#how-do-you-manipulate-dom-using-a-service-worker) |
| 33 | [How do you reuse information across service worker restarts](#how-do-you-reuse-information-across-service-worker-restarts) |
| 34 | [What is IndexedDB](#what-is-indexeddb) |
| 35 | [What is web storage](#what-is-web-storage) |
| 36 | [What is a post message](#what-is-a-post-message) |
| 37 | [What is a cookie](#what-is-a-cookie) |
| 38 | [Why do you need a Cookie](#why-do-you-need-a-cookie) |
| 39 | [What are the options in a cookie](#what-are-the-options-in-a-cookie) |
| 40 | [How do you delete a cookie](#how-do-you-delete-a-cookie) |
| 41 | [What are the differences between cookie, local storage and session storage](#What-are-the-differences-between-cookie-local-storage-and-session-storage) |
| 42 | [What is the main difference between localStorage and sessionStorage](#what-is-the-main-difference-between-localstorage-and-sessionstorage) |
| 43 | [How do you access web storage](#how-do-you-access-web-storage) |
| 44 | [What are the methods available on session storage](#what-are-the-methods-available-on-session-storage) |
| 45 | [What is a storage event and its event handler](#what-is-a-storage-event-and-its-event-handler) |
| 46 | [Why do you need web storage](#why-do-you-need-web-storage) |
| 47 | [How do you check web storage browser support](#how-do-you-check-web-storage-browser-support) |
| 48 | [How do you check web workers browser support](#how-do-you-check-web-workers-browser-support) |
| 49 | [Give an example of a web worker](#give-an-example-of-a-web-worker) |
| 50 | [What are the restrictions of web workers on DOM](#what-are-the-restrictions-of-web-workers-on-dom) |
| 51 | [What is a promise](#what-is-a-promise) |
| 52 | [Why do you need a promise](#why-do-you-need-a-promise) |
| 53 | [What are the three states of promise](#what-are-the-three-states-of-promise) |
| 54 | [What is a callback function](#what-is-a-callback-function) |
| 55 | [Why do we need callbacks](#why-do-we-need-callbacks) |
| 56 | [What is a callback hell](#what-is-a-callback-hell) |
| 57 | [What are server-sent events](#what-are-server-sent-events) |
| 58 | [How do you receive server-sent event notifications](#how-do-you-receive-server-sent-event-notifications) |
| 59 | [How do you check browser support for server-sent events](#how-do-you-check-browser-support-for-server-sent-events) |
| 60 | [What are the events available for server sent events](#what-are-the-events-available-for-server-sent-events) |
| 61 | [What are the main rules of promise](#what-are-the-main-rules-of-promise) |
| 62 | [What is callback in callback](#what-is-callback-in-callback) |
| 63 | [What is promise chaining](#what-is-promise-chaining) |
| 64 | [What is promise.all](#what-is-promiseall) |
| 65 | [What is the purpose of the race method in promise](#what-is-the-purpose-of-the-race-method-in-promise) |
| 66 | [What is a strict mode in javascript](#what-is-a-strict-mode-in-javascript) |
| 67 | [Why do you need strict mode](#why-do-you-need-strict-mode) |
| 68 | [How do you declare strict mode](#how-do-you-declare-strict-mode) |
| 69 | [What is the purpose of double exclamation](#what-is-the-purpose-of-double-exclamation) |
| 70 | [What is the purpose of the delete operator](#what-is-the-purpose-of-the-delete-operator) |
| 71 | [What is typeof operator](#what-is-typeof-operator) |
| 72 | [What is undefined property](#what-is-undefined-property) |
| 73 | [What is null value](#what-is-null-value) |
| 74 | [What is the difference between null and undefined](#what-is-the-difference-between-null-and-undefined) |
| 75 | [What is eval](#What-is-eval) |
| 76 | [What is the difference between window and document](#what-is-the-difference-between-window-and-document) |
| 77 | [How do you access history in javascript](#how-do-you-access-history-in-javascript) |
| 78 | [How do you detect caps lock key turned on or not](#how-do-you-detect-caps-lock-key-turned-on-or-not) |
| 79 | [What is isNaN](#what-is-isnan) |
| 80 | [What are the differences between undeclared and undefined variables](#what-are-the-differences-between-undeclared-and-undefined-variables) |
| 81 | [What are global variables](#what-are-global-variables) |
| 82 | [What are the problems with global variables](#what-are-the-problems-with-global-variables) |
| 83 | [What is NaN property](#what-is-nan-property) |
| 84 | [What is the purpose of isFinite function](#what-is-the-purpose-of-isfinite-function) |
| 85 | [What is an event flow](#what-is-an-event-flow) |
| 86 | [What is event bubbling](#what-is-event-bubbling) |
| 87 | [What is event capturing](#what-is-event-capturing) |
| 88 | [How do you submit a form using JavaScript](#how-do-you-submit-a-form-using-javascript) |
| 89 | [How do you find operating system details](#how-do-you-find-operating-system-details) |
| 90 | [What is the difference between document load and DOMContentLoaded events](#what-is-the-difference-between-document-load-and-domcontentloaded-events) |
| 91 | [What is the difference between native, host and user objects](#what-is-the-difference-between-native-host-and-user-objects) |
| 92 | [What are the tools or techniques used for debugging JavaScript code](#what-are-the-tools-or-techniques-used-for-debugging-javascript-code) |
| 93 | [What are the pros and cons of promises over callbacks](#what-are-the-pros-and-cons-of-promises-over-callbacks) |
| 94 | [What is the difference between an attribute and a property](#what-is-the-difference-between-an-attribute-and-a-property) |
| 95 | [What is same-origin policy](#what-is-same-origin-policy) |
| 96 | [What is the purpose of void 0](#what-is-the-purpose-of-void-0) |
| 97 | [Is JavaScript a compiled or interpreted language](#is-javascript-a-compiled-or-interpreted-language) |
| 98 | [Is JavaScript a case-sensitive language](#is-javascript-a-case-sensitive-language) |
| 99 | [Is there any relation between Java and JavaScript](#is-there-any-relation-between-java-and-javascript) |
| 100 | [What are events](#what-are-events) |
| 101 | [Who created javascript](#who-created-javascript) |
| 102 | [What is the use of preventDefault method](#what-is-the-use-of-preventdefault-method) |
| 103 | [What is the use of stopPropagation method](#what-is-the-use-of-stoppropagation-method) |
| 104 | [What are the steps involved in return false usage](#what-are-the-steps-involved-in-return-false-usage) |
| 105 | [What is BOM](#what-is-bom) |
| 106 | [What is the use of setTimeout](#what-is-the-use-of-settimeout) |
| 107 | [What is the use of setInterval](#what-is-the-use-of-setinterval) |
| 108 | [Why is JavaScript treated as Single threaded](#why-is-javascript-treated-as-single-threaded) |
| 109 | [What is an event delegation](#what-is-an-event-delegation) |
| 110 | [What is ECMAScript](#what-is-ecmascript) |
| 111 | [What is JSON](#what-is-json) |
| 112 | [What are the syntax rules of JSON](#what-are-the-syntax-rules-of-json) |
| 113 | [What is the purpose JSON stringify](#what-is-the-purpose-json-stringify) |
| 114 | [How do you parse JSON string](#how-do-you-parse-json-string) |
| 115 | [Why do you need JSON](#why-do-you-need-json) |
| 116 | [What are PWAs](#what-are-pwas) |
| 117 | [What is the purpose of clearTimeout method](#what-is-the-purpose-of-cleartimeout-method) |
| 118 | [What is the purpose of clearInterval method](#what-is-the-purpose-of-clearinterval-method) |
| 119 | [How do you redirect new page in javascript](#how-do-you-redirect-new-page-in-javascript) |
| 120 | [How do you check whether a string contains a substring](#how-do-you-check-whether-a-string-contains-a-substring) |
| 121 | [How do you validate an email in javascript](#how-do-you-validate-an-email-in-javascript) |
| 122 | [How do you get the current url with javascript](#how-do-you-get-the-current-url-with-javascript) |
| 123 | [What are the various url properties of location object](#what-are-the-various-url-properties-of-location-object) |
| 124 | [How do get query string values in javascript](#how-do-get-query-string-values-in-javascript) |
| 125 | [How do you check if a key exists in an object](#how-do-you-check-if-a-key-exists-in-an-object) |
| 126 | [How do you loop through or enumerate javascript object](#how-do-you-loop-through-or-enumerate-javascript-object) |
| 127 | [How do you test for an empty object](#how-do-you-test-for-an-empty-object) |
| 128 | [What is an arguments object](#what-is-an-arguments-object) |
| 129 | [How do you convert the first letter of a string to uppercase](#how-do-you-make-first-letter-of-the-string-in-an-uppercase) |
| 130 | [What are the pros and cons of for loop](#what-are-the-pros-and-cons-of-for-loop) |
| 131 | [How do you display the current date in javascript](#how-do-you-display-the-current-date-in-javascript) |
| 132 | [How do you compare two date objects](#how-do-you-compare-two-date-objects) |
| 133 | [How do you check if a string starts with another string](#how-do-you-check-if-a-string-starts-with-another-string) |
| 134 | [How do you trim a string in javascript](#how-do-you-trim-a-string-in-javascript) |
| 135 | [How do you add a key value pair in javascript](#how-do-you-add-a-key-value-pair-in-javascript) |
| 136 | [Is the '!--' notation represents a special operator](#is-the----notation-represents-a-special-operator) |
| 137 | [How do you assign default values to variables](#how-do-you-assign-default-values-to-variables) |
| 138 | [How do you define multiline strings](#how-do-you-define-multiline-strings) |
| 139 | [What is an app shell model](#what-is-an-app-shell-model) |
| 140 | [Can we define properties for functions](#can-we-define-properties-for-functions) |
| 141 | [What is the way to find the number of parameters expected by a function](#what-is-the-way-to-find-the-number-of-parameters-expected-by-a-function) |
| 142 | [What is a polyfill](#what-is-a-polyfill) |
| 143 | [What are break and continue statements](#what-are-break-and-continue-statements) |
| 144 | [What are js labels](#what-are-js-labels) |
| 145 | [What are the benefits of keeping declarations at the top](#what-are-the-benefits-of-keeping-declarations-at-the-top) |
| 146 | [What are the benefits of initializing variables](#what-are-the-benefits-of-initializing-variables) |
| 147 | [What are the recommendations to create new object](#what-are-the-recommendations-to-create-new-object) |
| 148 | [How do you define JSON arrays](#how-do-you-define-json-arrays) |
| 149 | [How do you generate random integers](#how-do-you-generate-random-integers) |
| 150 | [Can you write a random integers function to print integers with in a range](#can-you-write-a-random-integers-function-to-print-integers-with-in-a-range) |
| 151 | [What is tree shaking](#what-is-tree-shaking) |
| 152 | [What is the need of tree shaking](#what-is-the-need-of-tree-shaking) |
| 153 | [Is it recommended to use eval](#is-it-recommended-to-use-eval) |
| 154 | [What is a Regular Expression](#what-is-a-regular-expression) |
| 155 | [What are the string methods available in Regular expression](#what-are-the-string-methods-available-in-regular-expression) |
| 156 | [What are modifiers in regular expression](#what-are-modifiers-in-regular-expression) |
| 157 | [What are regular expression patterns](#what-are-regular-expression-patterns) |
| 158 | [What is a RegExp object](#what-is-a-regexp-object) |
| 159 | [How do you search a string for a pattern](#how-do-you-search-a-string-for-a-pattern) |
| 160 | [What is the purpose of exec method](#what-is-the-purpose-of-exec-method) |
| 161 | [How do you change the style of a HTML element](#how-do-you-change-the-style-of-a-html-element) |
| 162 | [What would be the result of 1+2+'3'](#what-would-be-the-result-of-123) |
| 163 | [What is a debugger statement](#what-is-a-debugger-statement) |
| 164 | [What is the purpose of breakpoints in debugging](#what-is-the-purpose-of-breakpoints-in-debugging) |
| 165 | [Can I use reserved words as identifiers](#can-i-use-reserved-words-as-identifiers) |
| 166 | [How do you detect a mobile browser](#how-do-you-detect-a-mobile-browser) |
| 167 | [How do you detect a mobile browser without regexp](#how-do-you-detect-a-mobile-browser-without-regexp) |
| 168 | [How do you get the image width and height using JS](#how-do-you-get-the-image-width-and-height-using-js) |
| 169 | [How do you make synchronous HTTP request](#how-do-you-make-synchronous-http-request) |
| 170 | [How do you make asynchronous HTTP request](#how-do-you-make-asynchronous-http-request) |
| 171 | [How do you convert date to another timezone in javascript](#how-do-you-convert-date-to-another-timezone-in-javascript) |
| 172 | [What are the properties used to get size of window](#what-are-the-properties-used-to-get-size-of-window) |
| 173 | [What is a conditional operator in javascript](#what-is-a-conditional-operator-in-javascript) |
| 174 | [Can you apply chaining on conditional operator](#Can-you-apply-chaining-on-conditional-operator) |
| 175 | [What are the ways to execute javascript after page load](#what-are-the-ways-to-execute-javascript-after-page-load) |
| 176 | [What is the difference between proto and prototype](#what-is-the-difference-between-proto-and-prototype) |
| 177 | [Give an example where do you really need semicolon](#give-an-example-where-do-you-really-need-semicolon) |
| 178 | [What is a freeze method](#what-is-a-freeze-method) |
| 179 | [What is the purpose of freeze method](#what-is-the-purpose-of-freeze-method) |
| 180 | [Why do I need to use freeze method](#why-do-i-need-to-use-freeze-method) |
| 181 | [How do you detect a browser language preference](#how-do-you-detect-a-browser-language-preference) |
| 182 | [How to convert string to title case with javascript](#how-to-convert-string-to-title-case-with-javascript) |
| 183 | [How do you detect javascript disabled in the page](#how-do-you-detect-javascript-disabled-in-the-page) |
| 184 | [What are various operators supported by javascript](#what-are-various-operators-supported-by-javascript) |
| 185 | [What is a rest parameter](#what-is-a-rest-parameter) |
| 186 | [What happens if you do not use rest parameter as a last argument](#what-happens-if-you-do-not-use-rest-parameter-as-a-last-argument) |
| 187 | [What are the bitwise operators available in javascript](#what-are-the-bitwise-operators-available-in-javascript) |
| 188 | [What is a spread operator](#what-is-a-spread-operator) |
| 189 | [How do you determine whether object is frozen or not](#how-do-you-determine-whether-object-is-frozen-or-not) |
| 190 | [How do you determine two values same or not using object](#how-do-you-determine-two-values-same-or-not-using-object) |
| 191 | [What is the purpose of using object is method](#what-is-the-purpose-of-using-object-is-method) |
| 192 | [How do you copy properties from one object to other](#how-do-you-copy-properties-from-one-object-to-other) |
| 193 | [What are the applications of assign method](#what-are-the-applications-of-assign-method) |
| 194 | [What is a proxy object](#what-is-a-proxy-object) |
| 195 | [What is the purpose of seal method](#what-is-the-purpose-of-seal-method) |
| 196 | [What are the applications of seal method](#what-are-the-applications-of-seal-method) |
| 197 | [What are the differences between freeze and seal methods](#what-are-the-differences-between-freeze-and-seal-methods) |
| 198 | [How do you determine if an object is sealed or not](#how-do-you-determine-if-an-object-is-sealed-or-not) |
| 199 | [How do you get enumerable key and value pairs](#how-do-you-get-enumerable-key-and-value-pairs) |
| 200 | [What is the main difference between Object.values and Object.entries method](#what-is-the-main-difference-between-objectvalues-and-objectentries-method) |
| 201 | [How can you get the list of keys of any object](#how-can-you-get-the-list-of-keys-of-any-object) |
| 202 | [How do you create an object with prototype](#how-do-you-create-an-object-with-prototype) |
| 203 | [What is a WeakSet](#what-is-a-weakset) |
| 204 | [What are the differences between a WeakSet and a Set](#what-are-the-differences-between-weakset-and-set) |
| 205 | [List down the collection of methods available on WeakSet](#list-down-the-collection-of-methods-available-on-weakset) |
| 206 | [What is a WeakMap](#what-is-a-weakmap) |
| 207 | [What are the differences between a WeakMap and a Map](#what-are-the-differences-between-weakmap-and-map) |
| 208 | [List down the collection of methods available on WeakMap](#list-down-the-collection-of-methods-available-on-weakmap) |
| 209 | [What is the purpose of uneval](#what-is-the-purpose-of-uneval) |
| 210 | [How do you encode an URL](#how-do-you-encode-an-url) |
| 211 | [How do you decode an URL](#how-do-you-decode-an-url) |
| 212 | [How do you print the contents of web page](#how-do-you-print-the-contents-of-web-page) |
| 213 | [What is the difference between uneval and eval](#what-is-the-difference-between-uneval-and-eval) |
| 214 | [What is an anonymous function](#what-is-an-anonymous-function) |
| 215 | [What is the precedence order between local and global variables](#what-is-the-precedence-order-between-local-and-global-variables) |
| 216 | [What are javascript accessors](#what-are-javascript-accessors) |
| 217 | [How do you define property on Object constructor](#how-do-you-define-property-on-object-constructor) |
| 218 | [What is the difference between get and defineProperty](#what-is-the-difference-between-get-and-defineproperty) |
| 219 | [What are the advantages of Getters and Setters](#what-are-the-advantages-of-getters-and-setters) |
| 220 | [Can I add getters and setters using defineProperty method](#can-i-add-getters-and-setters-using-defineproperty-method) |
| 221 | [What is the purpose of switch-case](#what-is-the-purpose-of-switch-case) |
| 222 | [What are the conventions to be followed for the usage of switch case](#what-are-the-conventions-to-be-followed-for-the-usage-of-switch-case) |
| 223 | [What are primitive data types](#what-are-primitive-data-types) |
| 224 | [What are the different ways to access object properties](#what-are-the-different-ways-to-access-object-properties) |
| 225 | [What are the function parameter rules](#what-are-the-function-parameter-rules) |
| 226 | [What is an error object](#what-is-an-error-object) |
| 227 | [When you get a syntax error](#when-you-get-a-syntax-error) |
| 228 | [What are the different error names from error object](#what-are-the-different-error-names-from-error-object) |
| 229 | [What are the various statements in error handling](#what-are-the-various-statements-in-error-handling) |
| 230 | [What are the two types of loops in javascript](#what-are-the-two-types-of-loops-in-javascript) |
| 231 | [What is nodejs](#what-is-nodejs) |
| 232 | [What is an Intl object](#what-is-an-intl-object) |
| 233 | [How do you perform language specific date and time formatting](#how-do-you-perform-language-specific-date-and-time-formatting) |
| 234 | [What is an Iterator](#what-is-an-iterator) |
| 235 | [How does the synchronous iteration work](#how-does-synchronous-iteration-works) |
| 236 | [What is an event loop](#what-is-an-event-loop) |
| 237 | [What is call stack](#what-is-call-stack) |
| 238 | [What is an event queue](#what-is-an-event-queue) |
| 239 | [What is a decorator](#what-is-a-decorator) |
| 240 | [What are the properties of Intl object](#what-are-the-properties-of-intl-object) |
| 241 | [What is an Unary operator](#what-is-an-unary-operator) |
| 242 | [How do you sort elements in an array](#how-do-you-sort-elements-in-an-array) |
| 243 | [What is the purpose of compareFunction while sorting arrays](#what-is-the-purpose-of-comparefunction-while-sorting-arrays) |
| 244 | [How do you reversing an array](#how-do-you-reversing-an-array) |
| 245 | [How do you find min and max value in an array](#how-do-you-find-min-and-max-value-in-an-array) |
| 246 | [How do you find min and max values without Math functions](#how-do-you-find-min-and-max-values-without-math-functions) |
| 247 | [What is an empty statement and purpose of it](#what-is-an-empty-statement-and-purpose-of-it) |
| 248 | [How do you get metadata of a module](#how-do-you-get-metadata-of-a-module) |
| 249 | [What is a comma operator](#what-is-a-comma-operator) |
| 250 | [What is the advantage of a comma operator](#what-is-the-advantage-of-a-comma-operator) |
| 251 | [What is typescript](#what-is-typescript) |
| 252 | [What are the differences between javascript and typescript](#what-are-the-differences-between-javascript-and-typescript) |
| 253 | [What are the advantages of typescript over javascript](#what-are-the-advantages-of-typescript-over-javascript) |
| 254 | [What is an object initializer](#what-is-an-object-initializer) |
| 255 | [What is a constructor method](#what-is-a-constructor-method) |
| 256 | [What happens if you write constructor more than once in a class](#what-happens-if-you-write-constructor-more-than-once-in-a-class) |
| 257 | [How do you call the constructor of a parent class](#how-do-you-call-the-constructor-of-a-parent-class) |
| 258 | [How do you get the prototype of an object](#how-do-you-get-the-prototype-of-an-object) |
| 259 | [What happens If I pass string type for getPrototype method](#what-happens-if-i-pass-string-type-for-getprototype-method) |
| 260 | [How do you set prototype of one object to another](#how-do-you-set-prototype-of-one-object-to-another) |
| 261 | [How do you check whether an object can be extendable or not](#how-do-you-check-whether-an-object-can-be-extendable-or-not) |
| 262 | [How do you prevent an object to extend](#how-do-you-prevent-an-object-to-extend) |
| 263 | [What are the different ways to make an object non-extensible](#what-are-the-different-ways-to-make-an-object-non-extensible) |
| 264 | [How do you define multiple properties on an object](#how-do-you-define-multiple-properties-on-an-object) |
| 265 | [What is MEAN in javascript](#what-is-mean-in-javascript) |
| 266 | [What Is Obfuscation in javascript](#what-is-obfuscation-in-javascript) |
| 267 | [Why do you need Obfuscation](#why-do-you-need-obfuscation) |
| 268 | [What is Minification](#what-is-minification) |
| 269 | [What are the advantages of minification](#what-are-the-advantages-of-minification) |
| 270 | [What are the differences between Obfuscation and Encryption](#what-are-the-differences-between-obfuscation-and-encryption) |
| 271 | [What are the common tools used for minification](#what-are-the-common-tools-used-for-minification) |
| 272 | [How do you perform form validation using javascript](#how-do-you-perform-form-validation-using-javascript) |
| 273 | [How do you perform form validation without javascript](#how-do-you-perform-form-validation-without-javascript) |
| 274 | [What are the DOM methods available for constraint validation](#what-are-the-dom-methods-available-for-constraint-validation) |
| 275 | [What are the available constraint validation DOM properties](#what-are-the-available-constraint-validation-dom-properties) |
| 276 | [What are the list of validity properties](#what-are-the-list-of-validity-properties) |
| 277 | [Give an example usage of rangeOverflow property](#give-an-example-usage-of-rangeoverflow-property) |
| 278 | [Is enums feature available in javascript](#is-enums-feature-available-in-javascript) |
| 279 | [What is an enum](#What-is-an-enum) |
| 280 | [How do you list all properties of an object](#how-do-you-list-all-properties-of-an-object) |
| 281 | [How do you get property descriptors of an object](#how-do-you-get-property-descriptors-of-an-object) |
| 282 | [What are the attributes provided by a property descriptor](#what-are-the-attributes-provided-by-a-property-descriptor) |
| 283 | [How do you extend classes](#how-do-you-extend-classes) |
| 284 | [How do I modify the url without reloading the page](#how-do-i-modify-the-url-without-reloading-the-page) |
| 285 | [How do you check whether an array includes a particular value or not](#how-do-you-check-whether-an-array-includes-a-particular-value-or-not) |
| 286 | [How do you compare scalar arrays](#how-do-you-compare-scalar-arrays) |
| 287 | [How to get the value from get parameters](#how-to-get-the-value-from-get-parameters) |
| 288 | [How do you print numbers with commas as thousand separators](#how-do-you-print-numbers-with-commas-as-thousand-separators) |
| 289 | [What is the difference between java and javascript](#what-is-the-difference-between-java-and-javascript) |
| 290 | [Does javascript supports namespace](#does-javascript-supports-namespace) |
| 291 | [How do you declare namespace](#how-do-you-declare-namespace) |
| 292 | [How do you invoke javascript code in an iframe from parent page](#how-do-you-invoke-javascript-code-in-an-iframe-from-parent-page) |
| 293 | [How do get the timezone offset from date](#how-do-get-the-timezone-offset-from-date) |
| 294 | [How do you load CSS and JS files dynamically](#how-do-you-load-css-and-js-files-dynamically) |
| 295 | [What are the different methods to find HTML elements in DOM](#what-are-the-different-methods-to-find-html-elements-in-dom) |
| 296 | [What is jQuery](#what-is-jquery) |
| 297 | [What is V8 JavaScript engine](#what-is-v8-javascript-engine) |
| 298 | [Why do we call javascript as dynamic language](#why-do-we-call-javascript-as-dynamic-language) |
| 299 | [What is a void operator](#what-is-a-void-operator) |
| 300 | [How to set the cursor to wait](#how-to-set-the-cursor-to-wait) |
| 301 | [How do you create an infinite loop](#how-do-you-create-an-infinite-loop) |
| 302 | [Why do you need to avoid with statement](#why-do-you-need-to-avoid-with-statement) |
| 303 | [What is the output of below for loops](#what-is-the-output-of-below-for-loops) |
| 304 | [List down some of the features of ES6](#list-down-some-of-the-features-of-es6) |
| 305 | [What is ES6](#what-is-es6) |
| 306 | [Can I redeclare let and const variables](#can-I-redeclare-let-and-const-variables) |
| 307 | [Is const variable makes the value immutable](#is-const-variable-makes-the-value-immutable) |
| 308 | [What are default parameters](#what-are-default-parameters) |
| 309 | [What are template literals](#what-are-template-literals) |
| 310 | [How do you write multi-line strings in template literals](#how-do-you-write-multi-line-strings-in-template-literals) |
| 311 | [What are nesting templates](#what-are-nesting-templates) |
| 312 | [What are tagged templates](#what-are-tagged-templates) |
| 313 | [What are raw strings](#what-are-raw-strings) |
| 314 | [What is destructuring assignment](#what-is-destructuring-assignment) |
| 315 | [What are default values in destructuring assignment](#what-are-default-values-in-destructuring-assignment) |
| 316 | [How do you swap variables in destructuring assignment](#how-do-you-swap-variables-in-destructuring-assignment) |
| 317 | [What are enhanced object literals](#what-are-enhanced-object-literals) |
| 318 | [What are dynamic imports](#what-are-dynamic-imports) |
| 319 | [What are the use cases for dynamic imports](#what-are-the-use-cases-for-dynamic-imports) |
| 320 | [What are typed arrays](#what-are-typed-arrays) |
| 321 | [What are the advantages of module loaders](#what-are-the-advantages-of-module-loaders) |
| 322 | [What is collation](#what-is-collation) |
| 323 | [What is for...of statement](#what-is-forof-statement) |
| 324 | [What is the output of below spread operator array](#what-is-the-output-of-below-spread-operator-array) |
| 325 | [Is PostMessage secure](#is-postmessage-secure) |
| 326 | [What are the problems with postmessage target origin as wildcard](#what-are-the-problems-with-postmessage-target-origin-as-wildcard) |
| 327 | [How do you avoid receiving postMessages from attackers](#how-do-you-avoid-receiving-postmessages-from-attackers) |
| 328 | [Can I avoid using postMessages completely](#can-i-avoid-using-postmessages-completely) |
| 329 | [Is postMessages synchronous](#is-postmessages-synchronous) |
| 330 | [What paradigm is Javascript](#what-paradigm-is-javascript) |
| 331 | [What is the difference between internal and external javascript](#what-is-the-difference-between-internal-and-external-javascript) |
| 332 | [Is JavaScript faster than server side script](#is-javascript-faster-than-server-side-script) |
| 333 | [How do you get the status of a checkbox](#how-do-you-get-the-status-of-a-checkbox) |
| 334 | [What is the purpose of double tilde operator](#what-is-the-purpose-of-double-tilde-operator) |
| 335 | [How do you convert character to ASCII code](#how-do-you-convert-character-to-ascii-code) |
| 336 | [What is ArrayBuffer](#what-is-arraybuffer) |
| 337 | [What is the output of below string expression](#what-is-the-output-of-below-string-expression) |
| 338 | [What is the purpose of Error object](#what-is-the-purpose-of-error-object) |
| 339 | [What is the purpose of EvalError object](#what-is-the-purpose-of-evalerror-object) |
| 340 | [What are the list of cases error thrown from non-strict mode to strict mode](#what-are-the-list-of-cases-error-thrown-from-non-strict-mode-to-strict-mode) |
| 341 | [Do all objects have prototypes](#do-all-objects-have-prototypes) |
| 342 | [What is the difference between a parameter and an argument](#what-is-the-difference-between-a-parameter-and-an-argument) |
| 343 | [What is the purpose of some method in arrays](#what-is-the-purpose-of-some-method-in-arrays) |
| 344 | [How do you combine two or more arrays](#how-do-you-combine-two-or-more-arrays) |
| 345 | [What is the difference between Shallow and Deep copy](#what-is-the-difference-between-shallow-and-deep-copy) |
| 346 | [How do you create specific number of copies of a string](#how-do-you-create-specific-number-of-copies-of-a-string) |
| 347 | [How do you return all matching strings against a regular expression](#how-do-you-return-all-matching-strings-against-a-regular-expression) |
| 348 | [How do you trim a string at the beginning or ending](#how-do-you-trim-a-string-at-the-beginning-or-ending) |
| 349 | [What is the output of below console statement with unary operator](#what-is-the-output-of-below-console-statement-with-unary-operator) |
| 350 | [Does javascript uses mixins](#does-javascript-uses-mixins) |
| 351 | [What is a thunk function](#what-is-a-thunk-function) |
| 352 | [What are asynchronous thunks](#what-are-asynchronous-thunks) |
| 353 | [What is the output of below function calls](#what-is-the-output-of-below-function-calls) |
| 354 | [How to remove all line breaks from a string](#how-to-remove-all-line-breaks-from-a-string) |
| 355 | [What is the difference between reflow and repaint](#what-is-the-difference-between-reflow-and-repaint) |
| 356 | [What happens with negating an array](#what-happens-with-negating-an-array) |
| 357 | [What happens if we add two arrays](#what-happens-if-we-add-two-arrays) |
| 358 | [What is the output of prepend additive operator on falsy values](#what-is-the-output-of-prepend-additive-operator-on-falsy-values) |
| 359 | [How do you create self string using special characters](#how-do-you-create-self-string-using-special-characters) |
| 360 | [How do you remove falsy values from an array](#how-do-you-remove-falsy-values-from-an-array) |
| 361 | [How do you get unique values of an array](#how-do-you-get-unique-values-of-an-array) |
| 362 | [What is destructuring aliases](#what-is-destructuring-aliases) |
| 363 | [How do you map the array values without using map method](#how-do-you-map-the-array-values-without-using-map-method) |
| 364 | [How do you empty an array](#how-do-you-empty-an-array) |
| 365 | [How do you round numbers to certain decimals](#how-do-you-rounding-numbers-to-certain-decimals) |
| 366 | [What is the easiest way to convert an array to an object](#what-is-the-easiest-way-to-convert-an-array-to-an-object) |
| 367 | [How do you create an array with some data](#how-do-you-create-an-array-with-some-data) |
| 368 | [What are the placeholders from console object](#what-are-the-placeholders-from-console-object) |
| 369 | [Is it possible to add CSS to console messages](#is-it-possible-to-add-css-to-console-messages) |
| 370 | [What is the purpose of dir method of console object](#what-is-the-purpose-of-dir-method-of-console-object) |
| 371 | [Is it possible to debug HTML elements in console](#is-it-possible-to-debug-html-elements-in-console) |
| 372 | [How do you display data in a tabular format using console object](#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](#how-do-you-verify-that-an-argument-is-a-number-or-not) |
| 374 | [How do you create copy to clipboard button](#how-do-you-create-copy-to-clipboard-button) |
| 375 | [What is the shortcut to get timestamp](#what-is-the-shortcut-to-get-timestamp) |
| 376 | [How do you flattening multi dimensional arrays](#how-do-you-flattening-multi-dimensional-arrays) |
| 377 | [What is the easiest multi condition checking](#what-is-the-easiest-multi-condition-checking) |
| 378 | [How do you capture browser back button](#how-do-you-capture-browser-back-button) |
| 379 | [How do you disable right click in the web page](#how-do-you-disable-right-click-in-the-web-page) |
| 380 | [What are wrapper objects](#what-are-wrapper-objects) |
| 381 | [What is AJAX](#what-is-ajax) |
| 382 | [What are the different ways to deal with Asynchronous Code](#what-are-the-different-ways-to-deal-with-asynchronous-code) |
| 383 | [How to cancel a fetch request](#how-to-cancel-a-fetch-request) |
| 384 | [What is web speech API](#what-is-web-speech-api) |
| 385 | [What is minimum timeout throttling](#what-is-minimum-timeout-throttling) |
| 386 | [How do you implement zero timeout in modern browsers](#how-do-you-implement-zero-timeout-in-modern-browsers) |
| 387 | [What are tasks in event loop](#what-are-tasks-in-event-loop) |
| 388 | [What is microtask](#what-is-microtask) |
| 389 | [What are different event loops](#what-are-different-event-loops) |
| 390 | [What is the purpose of queueMicrotask](#what-is-the-purpose-of-queuemicrotask) |
| 391 | [How do you use javascript libraries in typescript file](#how-do-you-use-javascript-libraries-in-typescript-file) |
| 392 | [What are the differences between promises and observables](#what-are-the-differences-between-promises-and-observables) |
| 393 | [What is heap](#what-is-heap) |
| 394 | [What is an event table](#what-is-an-event-table) |
| 395 | [What is a microTask queue](#what-is-a-microtask-queue) |
| 396 | [What is the difference between shim and polyfill](#what-is-the-difference-between-shim-and-polyfill) |
| 397 | [How do you detect primitive or non primitive value type](#how-do-you-detect-primitive-or-non-primitive-value-type) |
| 398 | [What is babel](#what-is-babel) |
| 399 | [Is Node.js completely single threaded](#is-nodejs-completely-single-threaded) |
| 400 | [What are the common use cases of observables](#what-are-the-common-use-cases-of-observables) |
| 401 | [What is RxJS](#what-is-rxjs) |
| 402 | [What is the difference between Function constructor and function declaration](#what-is-the-difference-between-function-constructor-and-function-declaration) |
| 403 | [What is a Short circuit condition](#what-is-a-short-circuit-condition) |
| 404 | [What is the easiest way to resize an array](#what-is-the-easiest-way-to-resize-an-array) |
| 405 | [What is an observable](#what-is-an-observable) |
| 406 | [What is the difference between function and class declarations](#what-is-the-difference-between-function-and-class-declarations) |
| 407 | [What is an async function](#what-is-an-async-function) |
| 408 | [How do you prevent promises swallowing errors](#how-do-you-prevent-promises-swallowing-errors) |
| 409 | [What is deno](#what-is-deno) |
| 410 | [How do you make an object iterable in javascript](#how-do-you-make-an-object-iterable-in-javascript) |
| 411 | [What is a Proper Tail Call](#what-is-a-proper-tail-call) |
| 412 | [How do you check an object is a promise or not](#how-do-you-check-an-object-is-a-promise-or-not) |
| 413 | [How to detect if a function is called as constructor](#how-to-detect-if-a-function-is-called-as-constructor) |
| 414 | [What are the differences between arguments object and rest parameter](#what-are-the-differences-between-arguments-object-and-rest-parameter) |
| 415 | [What are the differences between spread operator and rest parameter](#what-are-the-differences-between-spread-operator-and-rest-parameter) |
| 416 | [What are the different kinds of generators](#what-are-the-different-kinds-of-generators) |
| 417 | [What are the built-in iterables](#what-are-the-built-in-iterables) |
| 418 | [What are the differences between for...of and for...in statements](#what-are-the-differences-between-forof-and-forin-statements) |
| 419 | [How do you define instance and non-instance properties](#how-do-you-define-instance-and-non-instance-properties) |
| 420 | [What is the difference between isNaN and Number.isNaN?](#what-is-the-difference-between-isnan-and-numberisnan) |
| 421 | [How to invoke an IIFE without any extra brackets?](#how-to-invoke-an-iife-without-any-extra-brackets) |
| 422 | [Is that possible to use expressions in switch cases?](#is-that-possible-to-use-expressions-in-switch-cases) |
| 423 | [What is the easiest way to ignore promise errors?](#what-is-the-easiest-way-to-ignore-promise-errors) |
| 424 | [How do style the console output using CSS?](#how-do-style-the-console-output-using-css) |
| 425 | [What is nullish coalescing operator (??)?](#what-is-nullish-coalescing-operator) |
| 426 | [How do you group and nest console output?](#how-do-you-group-and-nest-console-output) |
| 427 | [What is the difference between dense and sparse arrays?](#what-is-the-difference-between-dense-and-sparse-arrays) |
| 428 | [What are the different ways to create sparse arrays?](#what-are-the-different-ways-to-create-sparse-arrays) |
| 429 | [What is the difference between setTimeout, setImmediate and process.nextTick?](#what-is-the-difference-between-settimeout-setimmediate-and-processnexttick) |
| 430 | [How do you reverse an array without modifying original array?](#how-do-you-reverse-an-array-without-modifying-original-array) |
| 431 | [How do you create custom HTML element?](#how-do-you-create-custom-html-element) |
| 432 | [What is global execution context?](#what-is-global-execution-context) |
| 433 | [What is function execution context?](#what-is-function-execution-context) |
| 434 | [What is debouncing?](#what-is-debouncing) |
| 435 | [What is throttling?](#what-is-throttling) |
| 436 | [What is optional chaining?](#what-is-optional-chaining) |
| 437 | [What is an environment record?](#what-is-an-environment-record) |
| 438 | [How to verify if a variable is an array?](#how-to-verify-if-a-variable-is-an-array) |
| 439 | [What is pass by value and pass by reference?](#what-is-pass-by-value-and-pass-by-reference) |
| 440 | [What are the differences between primitives and non-primitives?](#what-are-the-differences-between-primitives-and-non-primitives) |
| 441 | [What are hidden classes?](#what-are-hidden-classes) |
| 442 | [What is inline caching?](#what-is-inline-caching) |
| 443 | [How do you create your own bind method using either call or apply method?](#how-do-you-create-your-own-bind-method-using-either-call-or-apply-method) |
| 444 | [What are the differences between pure and impure functions?](#what-are-the-differences-between-pure-and-impure-functions?) |
| 445 | [What is referential transparency?](#what-is-referential-transparency) |
| 446 | [What are the possible side-effects in javascript?](#what-are-the-possible-side-effects-in-javascript) |
| 447 | [What are compose and pipe functions?](#what-are-compose-and-pipe-functions) |
| 448 | [What is module pattern?](#what-is-module-pattern) |
| 449 | [What is Function Composition?](#what-is-function-composition) |
| 450 | [How to use await outside of async function prior to ES2022?](#how-to-use-await-outside-of-async-function-prior-to-es2022) |
| 451 | [What is the purpose of the this keyword in JavaScript?](#what_is_the_purpose_of_the_this_keyword_in_javascript?) |
| 452 | [What are the advantages of closures?](#what-are-the-advantages-of-closures) |
| 453 | [What are the phases of execution context?](#what-are-the-phases-of-execution-context) |
| 454 | [What are the possible reasons for memory leaks?](#what-are-the-possible-reasons-for-memory-leaks) |
| 455 | [What are the optimization techniques of V8 engine?](#what-are-the-optimization-techniques-of-v8-engine) |
| 456 | [What are the examples of built-in higher order functions??](#what-are-the-examples-of-built-in-higher-order-functions) |
| 457 | [What are the benefits higher order functions??](#what-are-the-benefits-higher-order-functions) |
| 458 | [How do you create polyfills for map, filter and reduce methods?](#how-do-you-create-polyfills-for-map-filter-and-reduce-functions) |
| 459 | [What is the difference between map and forEach functions?](#what-is-the-difference-between-map-and-foreach-functions) |
| 460 | [Give an example of statements affected by automatic semicolon insertion?](#give-an-example-of-statements-affected-by-automatic-semicolon-insertion) |
|461| [What are the event phases on browser?](#what-are-the-event-phases-on-browser) |
|462| [What are the real world usecases of proxy?](#what-are-the-real-world-usecases-of-proxy) |
1. ### What are the possible ways to create objects in JavaScript
There are many ways to create objects in javascript as mentioned below:
1. **Object literal syntax:**
The object literal syntax (or object initializer), is a comma-separated set of name-value pairs wrapped in curly braces.
```javascript
var object = {
name: "Sudheer",
age: 34
};
```
Object literal property values can be of any data type, including array, function, and nested object.
**Note:** This is one of the easiest ways to create an object.
2. **Object constructor:**
The simplest way to create an empty object is using the `Object` constructor. Currently this approach is not recommended.
```javascript
var object = new Object();
```
The `Object()` is a built-in constructor function so "new" keyword is not required. The above code snippet can be re-written as:
```javascript
var object = Object();
```
3. **Object's create method:**
The `create` method of Object is used to create a new object by passing the specificied prototype object and properties as arguments, i.e., this pattern is helpful to create new objects based on existing objects.
The second argument is optional and it is used to create properties on a newly created object.
The following code creates a new empty object whose prototype is null.
```javascript
var object = Object.create(null);
```
The following example creates an object along with additional new properties.
```javascript
let vehicle = {
wheels: '4',
fuelType: 'Gasoline',
color: 'Green'
}
let carProps = {
type: {
value: 'Volkswagen'
},
model: {
value: 'Golf'
}
}
var car = Object.create(vehicle, carProps);
console.log(car);
```
4. **Function constructor:**
In this approach, create any function and apply the new operator to create object instances.
```javascript
function Person(name) {
this.name = name;
this.age = 21;
}
var object = new Person("Sudheer");
```
5. **Function constructor with prototype:**
This is similar to function constructor but it uses prototype for their properties and methods,
```javascript
function Person() {}
Person.prototype.name = "Sudheer";
var object = new Person();
```
This is equivalent to creating an instance with Object.create method with a function prototype and then calling that function with an instance and parameters as arguments.
```javascript
function func() {}
new func(x, y, z);
```
**(OR)**
```javascript
// Create a new instance using function prototype.
var newInstance = Object.create(func.prototype)
// Call the function
var result = func.call(newInstance, x, y, z),
// If the result is a non-null object then use it otherwise just use the new instance.
console.log(result && typeof result === 'object' ? result : newInstance);
```
6. **Object's assign method:**
The `Object.assign` method is used to copy all the properties from one or more source objects and stores them into a target object.
The following code creates a new staff object by copying properties of his working company and the car he owns.
```javascript
const orgObject = { company: 'XYZ Corp'};
const carObject = { name: 'Toyota'};
const staff = Object.assign({}, orgObject, carObject);
```
7. **ES6 Class syntax:**
ES6 introduces class feature to create objects.
```javascript
class Person {
constructor(name) {
this.name = name;
}
}
var object = new Person("Sudheer");
```
8. **Singleton pattern:**
A Singleton is an object which can only be instantiated one time. Repeated calls to its constructor return the same instance. This way one can ensure that they don't accidentally create multiple instances.
```javascript
var object = new (function () {
this.name = "Sudheer";
})();
```
**[⬆ Back to Top](#table-of-contents)**
2. ### What is a prototype chain
**Prototype chaining** is used to build new types of objects based on existing ones. It is similar to inheritance in a class based language.
The prototype on object instance is available through **Object.getPrototypeOf(object)** or **\_\_proto\_\_** property whereas prototype on constructors function is available through **Object.prototype**.
**[⬆ Back to Top](#table-of-contents)**
3. ### What is the difference between Call, Apply and Bind
The difference between Call, Apply and Bind can be explained with below examples,
**Call:** The call() method invokes a function with a given `this` value and arguments provided one by one
```javascript
var employee1 = { firstName: "John", lastName: "Rodson" };
var employee2 = { firstName: "Jimmy", lastName: "Baily" };
function invite(greeting1, greeting2) {
console.log(
greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
);
}
invite.call(employee1, "Hello", "How are you?"); // Hello John Rodson, How are you?
invite.call(employee2, "Hello", "How are you?"); // Hello Jimmy Baily, How are you?
```
**Apply:** Invokes the function with a given `this` value and allows you to pass in arguments as an array
```javascript
var employee1 = { firstName: "John", lastName: "Rodson" };
var employee2 = { firstName: "Jimmy", lastName: "Baily" };
function invite(greeting1, greeting2) {
console.log(
greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
);
}
invite.apply(employee1, ["Hello", "How are you?"]); // Hello John Rodson, How are you?
invite.apply(employee2, ["Hello", "How are you?"]); // Hello Jimmy Baily, How are you?
```
**Bind:** returns a new function, allowing you to pass any number of arguments
```javascript
var employee1 = { firstName: "John", lastName: "Rodson" };
var employee2 = { firstName: "Jimmy", lastName: "Baily" };
function invite(greeting1, greeting2) {
console.log(
greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
);
}
var inviteEmployee1 = invite.bind(employee1);
var inviteEmployee2 = invite.bind(employee2);
inviteEmployee1("Hello", "How are you?"); // Hello John Rodson, How are you?
inviteEmployee2("Hello", "How are you?"); // Hello Jimmy Baily, How are you?
```
Call and Apply are pretty much interchangeable. Both execute the current function immediately. You need to decide whether it’s easier to send in an array or a comma separated list of arguments. You can remember by treating Call is for **comma** (separated list) and Apply is for **Array**.
Bind creates a new function that will have `this` set to the first parameter passed to bind().
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4. ### What is JSON and its common operations
**JSON** is a text-based data format following JavaScript object syntax, which was popularized by `Douglas Crockford`. It is useful when you want to transmit data across a network. It is basically just a text file with an extension of .json, and a MIME type of application/json
**Parsing:** Converting a string to a native object
```javascript
JSON.parse(text);
```
**Stringification:** Converting a native object to a string so that it can be transmitted across the network
```javascript
JSON.stringify(object);
```
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5. ### What is the purpose of the array slice method
The **slice()** method returns the selected elements in an array as a new array object. It selects the elements starting at the given start argument, and ends at the given optional end argument without including the last element. If you omit the second argument then it selects till the end of the array.
Some of the examples of this method are,
```javascript
let arrayIntegers = [1, 2, 3, 4, 5];
let arrayIntegers1 = arrayIntegers.slice(0, 2); // returns [1,2]
let arrayIntegers2 = arrayIntegers.slice(2, 3); // returns [3]
let arrayIntegers3 = arrayIntegers.slice(4); //returns [5]
```
**Note:** Slice method doesn't mutate the original array but it returns the subset as a new array.
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6. ### What is the purpose of the array splice method
The **splice()** method adds/removes items to/from an array, and then returns the removed item. The first argument specifies the array position/index for insertion or deletion whereas the optional second argument indicates the number of elements to be deleted. Each additional argument is added to the array.
Some of the examples of this method are:
```javascript
let arrayIntegersOriginal1 = [1, 2, 3, 4, 5];
let arrayIntegersOriginal2 = [1, 2, 3, 4, 5];
let arrayIntegersOriginal3 = [1, 2, 3, 4, 5];
let arrayIntegers1 = arrayIntegersOriginal1.splice(0, 2); // returns [1, 2]; original array: [3, 4, 5]
let arrayIntegers2 = arrayIntegersOriginal2.splice(3); // returns [4, 5]; original array: [1, 2, 3]
let arrayIntegers3 = arrayIntegersOriginal3.splice(3, 1, "a", "b", "c"); //returns [4]; original array: [1, 2, 3, "a", "b", "c", 5]
```
**Note:** Splice method modifies the original array and returns the deleted array.
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7. ### What is the difference between slice and splice
Some of the major differences in a tabular form:
| Slice | Splice |
| -------------------------------------------- | ----------------------------------------------- |
| Doesn't modify the original array(immutable) | Modifies the original array(mutable) |
| Returns the subset of original array | Returns the deleted elements as array |
| Used to pick the elements from array | Used to insert/delete elements to/from array |
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8. ### How do you compare Object and Map
**Objects** are similar to **Maps** in that both let you set keys to values, retrieve those values, delete keys, and detect whether something is stored at a key. Due to this reason, Objects have been used as Maps historically. But there are important differences that make using a Map preferable in certain cases:
1. The keys of an Object can be Strings and Symbols, whereas they can be any value for a Map, including functions, objects, and any primitive.
2. The keys in a Map are ordered while keys added to Object are not. Thus, when iterating over it, a Map object returns keys in the order of insertion.
3. You can get the size of a Map easily with the size property, while the number of properties in an Object must be determined manually.
4. A Map is an iterable and can thus be directly iterated, whereas iterating over an Object requires obtaining its keys in some fashion and iterating over them.
5. An Object has a prototype, so there are default keys in an object that could collide with your keys if you're not careful. As of ES5 this can be bypassed by creating an object(which can be called a map) using `Object.create(null)`, but this practice is seldom done.
6. A Map may perform better in scenarios involving frequent addition and removal of key pairs.
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9. ### What is the difference between == and === operators
JavaScript provides both strict(===, !==) and type-converting(==, !=) equality comparison. The strict operators take type of variable in consideration, while non-strict operators make type correction/conversion based upon values of variables. The strict operators follow the below conditions for different types,
1. Two strings are strictly equal when they have the same sequence of characters, same length, and same characters in corresponding positions.
2. Two numbers are strictly equal when they are numerically equal, i.e., having the same number value.
There are two special cases in this,
1. NaN is not equal to anything, including NaN.
2. Positive and negative zeros are equal to one another.
3. Two Boolean operands are strictly equal if both are true or both are false.
4. Two objects are strictly equal if they refer to the same Object.
5. Null and Undefined types are not equal with ===, but equal with == .
i.e, `null===undefined --> false`, but `null==undefined --> true`
Some of the example which covers the above cases:
```javascript
0 == false // true
0 === false // false
1 == "1" // true
1 === "1" // false
null == undefined // true
null === undefined // false
'0' == false // true
'0' === false // false
NaN == NaN or NaN === NaN // false
[]==[] or []===[] //false, refer different objects in memory
{}=={} or {}==={} //false, refer different objects in memory
```
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10. ### What are lambda expressions or arrow functions
An arrow function is a shorter/concise syntax for a function expression and does not have its own **this, arguments, super, or new.target**. These functions are best suited for non-method functions, and they cannot be used as constructors.
Some of the examples of arrow functions are listed as below,
```javascript
const arrowFunc1 = (a, b) => a + b; // Multiple parameters
const arrowFunc2 = a => a * 10; // Single parameter
const arrowFunc3 = () => {} // no parameters
```
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11. ### What is a first class function
In Javascript, functions are first class objects. First-class functions means when functions in that language are treated like any other variable.
For example, in such a language, a function can be passed as an argument to other functions, can be returned by another function and can be assigned as a value to a variable. For example, in the below example, handler functions assigned to a listener
```javascript
const handler = () => console.log("This is a click handler function");
document.addEventListener("click", handler);
```
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12. ### What is a first order function
A first-order function is a function that doesn’t accept another function as an argument and doesn’t return a function as its return value.
```javascript
const firstOrder = () => console.log("I am a first order function!");
```
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13. ### What is a higher order function
A higher-order function is a function that accepts another function as an argument or returns a function as a return value or both.
The syntactic structure of higher order function will be as follows,
```javascript
const firstOrderFunc = () =>
console.log("Hello, I am a First order function");
const higherOrder = (ReturnFirstOrderFunc) => ReturnFirstOrderFunc();
higherOrder(firstOrderFunc);
```
You can also call the function which you are passing to higher order function as callback function.
The higher order function is helpful to write the modular and reusable code. For example, the below example illustrate the
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14. ### What is a unary function
A unary function (i.e. monadic) is a function that accepts exactly one argument. It stands for a single argument accepted by a function.
Let us take an example of unary function,
```javascript
const unaryFunction = (a) => console.log(a + 10); // Add 10 to the given argument and display the value
```
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15. ### What is the currying function
Currying is the process of taking a function with multiple arguments and turning it into a sequence of functions each with only a single argument. Currying is named after a mathematician **Haskell Curry**. By applying currying, an n-ary function turns into a unary function.
Let's take an example of n-ary function and how it turns into a currying function,
```javascript
const multiArgFunction = (a, b, c) => a + b + c;
console.log(multiArgFunction(1, 2, 3)); // 6
const curryUnaryFunction = (a) => (b) => (c) => a + b + c;
curryUnaryFunction(1); // returns a function: b => c => 1 + b + c
curryUnaryFunction(1)(2); // returns a function: c => 3 + c
curryUnaryFunction(1)(2)(3); // returns the number 6
```
Curried functions are great to improve **code reusability** and **functional composition**.
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16. ### What is a pure function
A **Pure function** is a function where the return value is only determined by its arguments without any side effects. i.e, If you call a function with the same arguments 'n' number of times and 'n' number of places in the application then it will always return the same value.
Let's take an example to see the difference between pure and impure functions,
```javascript
//Impure
let numberArray = [];
const impureAddNumber = (number) => numberArray.push(number);
//Pure
const pureAddNumber = (number) => (argNumberArray) =>
argNumberArray.concat([number]);
//Display the results
console.log(impureAddNumber(6)); // returns 1
console.log(numberArray); // returns [6]
console.log(pureAddNumber(7)(numberArray)); // returns [6, 7]
console.log(numberArray); // returns [6]
```
As per the above code snippets, the **Push** function is impure itself by altering the array and returning a push number index independent of the parameter value, whereas **Concat** on the other hand takes the array and concatenates it with the other array producing a whole new array without side effects. Also, the return value is a concatenation of the previous array.
Remember that Pure functions are important as they simplify unit testing without any side effects and no need for dependency injection. They also avoid tight coupling and make it harder to break your application by not having any side effects. These principles are coming together with the **Immutability** concept of ES6: giving preference to **const** over **let** usage.
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17. ### What is the purpose of the let keyword
The `let` statement declares a **block scope local variable**. Hence the variables defined with let keyword are limited in scope to the block, statement, or expression on which it is used. Whereas variables declared with the `var` keyword used to define a variable globally, or locally to an entire function regardless of block scope.
Let's take an example to demonstrate the usage,
```javascript
let counter = 30;
if (counter === 30) {
let counter = 31;
console.log(counter); // 31
}
console.log(counter); // 30 (because the variable in if block won't exist here)
```
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18. ### What is the difference between let and var
You can list out the differences in a tabular format
| var | let |
| ----------------------------------------------------- | --------------------------- |
| It has been available from the beginning of JavaScript | Introduced as part of ES6 |
| It has function scope | It has block scope |
| Variable declaration will be hoisted | Hoisted but not initialized |
| It is possible to re-declare the variable in the same scope | It is not possible to re-declare the variable |
Let's take an example to see the difference,
```javascript
function userDetails(username) {
if (username) {
console.log(salary); // undefined due to hoisting
console.log(age); // ReferenceError: Cannot access 'age' before initialization
let age = 30;
var salary = 10000;
}
console.log(salary); //10000 (accessible due to function scope)
console.log(age); //error: age is not defined(due to block scope)
}
userDetails("John");
```
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19. ### What is the reason to choose the name let as a keyword
`let` is a mathematical statement that was adopted by early programming languages like **Scheme** and **Basic**. It has been borrowed from dozens of other languages that use `let` already as a traditional keyword as close to `var` as possible.
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20. ### How do you redeclare variables in a switch block without an error
If you try to redeclare variables in a `switch block` then it will cause errors because there is only one block. For example, the below code block throws a syntax error as below,
```javascript
let counter = 1;
switch (x) {
case 0:
let name;
break;
case 1:
let name; // SyntaxError for redeclaration.
break;
}
```
To avoid this error, you can create a nested block inside a case clause and create a new block scoped lexical environment.
```javascript
let counter = 1;
switch (x) {
case 0: {
let name;
break;
}
case 1: {
let name; // No SyntaxError for redeclaration.
break;
}
}
```
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21. ### What is the Temporal Dead Zone
The Temporal Dead Zone(TDZ) is a specific period or area of a block where a variable is inaccessible until it has been intialized with a value. This behavior in JavaScript that occurs when declaring a variable with the let and const keywords, but not with var. In ECMAScript 6, accessing a `let` or `const` variable before its declaration (within its scope) causes a ReferenceError.
Let's see this behavior with an example,
```javascript
function somemethod() {