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JavaScript interview questions

JavaScript interview questions.

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1.

What is the object type?

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2.

Explain arrays in JavaScript

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3.

What is typeof operator?

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4.

Explain equality in JavaScript

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5.

What is Scope in JavaScript?

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6.

Explain Values and Types in JavaScript

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7.

What is let keyword in JavaScript?

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8.

Explain the same-origin policy with regards to JavaScript.

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9.

What is the difference between == and ===?

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10.

Is there anyway to force using strict mode in Node.js?

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11.

Why would you use something like the load event? Does this event have disadvantages? Do you know any alternatives, and why would you use those?

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12.

What is strict mode?

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13.

What's the difference between Host objects and Native objects?

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14.

What language constructions do you use for iterating over object properties and array items?

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15.

What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript?

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16.

Explain event bubbling and how one may prevent it

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17.

What does use strict do?

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18.

Why is it, in general, a good idea to leave the global scope of a website as-is and never touch it?

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19.

What is a Polyfill?

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20.

Explain Null and Undefined in JavaScript

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21.

What's the difference between throw Error('msg') vs throw new Error('msg')?

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22.

Lucky sevens

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23.

Simple clock angle

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24.

Sum of several arrays

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25.

Test divisors of three

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26.

Oddball sum

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27.

Sum of Array Plus One

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28.

String Rotation

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29.

Make this work

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30.

Given a string, reverse each word in the sentence

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31.

Implement enqueue and dequeue using only two stacks

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32.

Write a "mul" function which will properly when invoked as below syntax

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33.

Explain what a callback function is and provide a simple example

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34.

How to empty an array in JavaScript?

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35.

Find the missing number in O(n) time

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36.

Write a function that would allow you to do this?

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37.

Remove duplicates of an array and return an array of only unique elements

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38.

How to check if an object is an array or not? Provide some code.

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39.

How would you check if a number is an integer?

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40.

Two sum problem

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41.

Determine overlapping numbers in ranges

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42.

Stock maximum profit

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43.

Tree Level Order Print

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44.

Step-by-step solution for step counting using recursion

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45.

Implement Bubble Sort

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46.

What is IIFEs (Immediately Invoked Function Expressions)?

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47.

What is Coercion in JavaScript?

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48.

What is the difference between a shim and a polyfill?

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49.

What is the definition of a Higher-Order Function?

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50.

What do you think of AMD vs CommonJS?

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51.

Explain the differences on the usage of foo between function foo() {} and var foo = function() {}

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52.

What is the drawback of creating true private in JavaScript?

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53.

What's the difference between .call and .apply?

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54.

What is the preferred syntax for defining enums in JavaScript?

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55.

Describe Closure concept in JavaScript as best as you could

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56.

Could you explain the difference between ES5 and ES6

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57.

When should we use generators in ES6?

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58.

Explain Function.prototype.bind.

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59.

What are the benefits of using spread syntax in ES6 and how is it different from rest syntax?

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60.

When should I use Arrow Functions in ES6?

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61.

Explain the difference between undefined and not defined in JavaScript

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62.

What are the advantages and disadvantages of using use strict?

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63.

What is Currying?

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64.

What are the differences between ES6 class and ES5 function constructors?

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65.

Why should we use ES6 classes?

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66.

Explain the difference between Object.freeze() vs const

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67.

How to compare two objects in JavaScript?

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68.

What will be the output of the following code?

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69.

What is a closure, and how/why would you use one?

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70.

What will be the output of the following code?

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71.

What's a typical use case for anonymous functions?

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72.

Suggest one simple way of removing duplicates from an array using ES6

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73.

What is generator in JS?

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74.

What is the difference between document load event and document DOMContentLoaded event?

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75.

What's the difference between using let and var to declare a variable in ES6?

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76.

What is the motivation for bringing Symbol to ES6?

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77.

Why is extending built-in JavaScript objects not a good idea?

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78.

What is the difference between Anonymous and Named functions?

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79.

Provide some examples of non-bulean value coercion to a boolean one

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80.

Given an array of integers, find the largest difference between two elements such that the element of lesser value must come before the greater element

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81.

What will the following code output?

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82.

Write a function that would allow you to do this

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83.

Given an array of integers, find the largest product yielded from three of the integers

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84.

What will be the output of the following code?

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85.

Check if a given string is a palindrome. Case sensitivity should be taken into account.

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86.

Find the intersection of two arrays

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87.

Write a recursive function that returns the binary string of a given decimal number

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88.

How would you use a closure to create a private counter?

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89.

FizzBuzz Challenge

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90.

Given two strings, return true if they are anagrams of one another

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91.

All Permutations (Anagrams) of a String

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92.

Find all string combinations consisting only of 0, 1 and ?

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93.

Generate all balanced bracket combinations

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94.

Implement a queue using two stacks

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95.

Throttle Function Implementation

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96.

Find Word Positions in Text

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97.

Merge two sorted linked lists

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98.

Dutch national flag sorting problem

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99.

Insert an interval into a list of sorted disjoint intervals

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100.

Implement a queue using a linked list

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101.

Quickly calculate the cube root of 6 digit numbers

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102.

Implement pow(a,b) without multiplication or division

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103.

What is the new keyword in JavaScript?

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104.

Explain Prototype Inheritance in JavaScript?

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105.

What does the term Transpiling stand for?

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106.

Can you give an example for destructuring an object or an array in ES6?

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107.

Explain the Prototype Design Pattern

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108.

Describe the JS module design pattern

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109.

Can you describe the main difference between a .forEach loop and a .map() loop and why you would pick one versus the other?

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110.

Explain what is Hoisting in Javascript

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111.

How can you share code between files?

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112.

What are the actual uses of ES6 WeakMap?

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113.

Explain difference between: function Person(){}, var person = Person(), and var person = new Person()?

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114.

Check if a given string is a isomorphic

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115.

What is Hoisting in JavaScript?

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116.

When should you NOT use arrow functions in ES6? Name three or more cases.

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117.

What's the difference between a variable that is: null, undefined or undeclared? How would you go about checking for any of these states?

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118.

What is the Temporal Dead Zone in ES6?

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119.

Explain how JSONP works (and how it's not really Ajax)

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120.

Could you compare usage of Module Pattern vs Constructor/Prototype pattern?

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121.

What's the difference between ES6 Map and WeakMap?

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122.

What is the difference between the await keyword and the yield keyword?

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123.

Compare Async/Await and Generators usage to achive same functionality

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124.

How to deep-freeze object in JavaScript?

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125.

Is it possible to reset an ECMAScript 6 generator to its initial state?

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126.

Is JavaScript a pass-by-reference or pass-by-value language?

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127.

In JavaScript, why is the this operator inconsistent?

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128.

Can you give an example of a curry function and why this syntax offers an advantage?

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129.

Write a recursive function that performs a binary search

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130.

When would you use the bind function?

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131.

Create a function that will evaluate if a given expression has balanced parentheses using stacks

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132.

How would you create a private variable in JavaScript?

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133.

How would you add your own method to the Array object so the following code would work?

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134.

How does the this keyword work? Provide some code examples

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135.

What will be the output of the following code?

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136.

Given an integer, determine if it is a power of 2. If so, return that number, else return -1

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137.

What will the following code output?

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138.

What will be the output of the following code?

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139.

Explain why the following doesn't work as an IIFE. What needs to be changed to properly make it an IIFE?

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140.

What is Closure in JavaScript? Provide an example

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141.

Transform Word

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142.

Describe the Revealing Module Pattern design pattern

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