Get Ready for Your JavaScript Interview: Top 100 Questions to Practice

JavaScript is a crucial skill for any developer, and mastering it can open doors to exciting career opportunities. Whether you're preparing for your first JavaScript interview or aiming to brush up on your skills, here are 100 essential questions that can help you ace your interview:

1. What is JavaScript?
2. What are the key differences between JavaScript and Java?
3. What are the data types in JavaScript?
4. Explain the concept of hoisting in JavaScript.
5. How does JavaScript handle asynchronous operations?
6. What are closures in JavaScript?
7. What is the prototype chain in JavaScript?
8. How do you check the type of a variable in JavaScript?
9. Explain the event bubbling and capturing in JavaScript.
10. How does prototypal inheritance differ from classical inheritance?
11. What is the difference between == and === operators?
12. How does setTimeout function work in JavaScript?
13. Explain the concept of promises in JavaScript.
14. What are arrow functions in JavaScript?
15. How does this keyword work in JavaScript?
16. What is the use of bind method in JavaScript?
17. How can you create a closure in JavaScript?
18. What is the difference between null and undefined?
19. Explain the concept of event delegation in JavaScript.
20. What is the difference between synchronous and asynchronous JavaScript?
21. How do you handle errors in JavaScript?
22. What are higher-order functions in JavaScript?
23. Explain the difference between function declaration and function expression.
24. How can you achieve inheritance in JavaScript?
25. What are the different ways to declare a variable in JavaScript?
26. Explain the use of map, filter, and reduce functions.
27. What is the purpose of JSON.stringify and JSON.parse in JavaScript?
28. How can you prevent the default behavior of an event in JavaScript?
29. Explain the concept of memoization in JavaScript.
30. What are the different types of scopes in JavaScript?
31. How does the ES6 module system differ from CommonJS?
32. What are the rest parameters in JavaScript?
33. How do you handle CORS in JavaScript?
34. Explain the use of async and await in JavaScript.
35. What are generator functions in JavaScript?
36. How can you convert a callback-based function to a promise-based function?
37. Explain the concept of currying in JavaScript.
38. What is the difference between let, const, and var in JavaScript?
39. How can you detect if a variable is an array in JavaScript?
40. Explain the purpose of the Symbol data type in JavaScript.
41. What is a closure trap in JavaScript?
42. How do you handle memory leaks in JavaScript?
43. Explain the use of try, catch, and finally in error handling.
44. What is the purpose of the use strict directive in JavaScript?
45. How can you check if an object has a property in JavaScript?
46. Explain the concept of event loop in JavaScript.
47. What are the differences between forEach and map methods?
48. How can you copy an object in JavaScript?
49. Explain the differences between slice and splice methods.
50. What is the purpose of the WeakMap and WeakSet in JavaScript?
51. How can you merge two arrays in JavaScript?
52. Explain the purpose of the Symbol.iterator method in JavaScript.
53. What are the different ways to create an object in JavaScript?
54. How can you validate an email address in JavaScript?
55. Explain the purpose of the includes method in arrays.
56. What are the differences between == and === operators in JavaScript?
57. How can you create a private variable in JavaScript?
58. Explain the purpose of the Object.keys method in JavaScript.
59. What are the differences between null, undefined, and undeclared in JavaScript?
60. How can you convert a string to a number in JavaScript?
61. Explain the purpose of the Array.isArray method in JavaScript.
62. What are the differences between function declaration and function expression in JavaScript?
63. How can you convert JSON to a JavaScript object?
64. Explain the purpose of the Array.prototype.map method in JavaScript.
65. What are the differences between let, const, and var in JavaScript?
66. How can you sort an array of objects by a specific property in JavaScript?
67. Explain the purpose of the Array.prototype.filter method in JavaScript.
68. What are the differences between == and === operators in JavaScript?
69. How can you remove duplicates from an array in JavaScript?
70. Explain the purpose of the Array.prototype.reduce method in JavaScript.
71. What are the differences between null, undefined, and undeclared in JavaScript?
72. How can you check if a string contains a substring in JavaScript?
73. Explain the purpose of the Array.prototype.forEach method in JavaScript.
74. What are the differences between let, const, and var in JavaScript?
75. How can you reverse a string in JavaScript?
76. Explain the purpose of the Array.prototype.indexOf method in JavaScript.
77. What are the differences between == and === operators in JavaScript?
78. How can you find the largest and smallest numbers in an array in JavaScript?
79. Explain the purpose of the Array.prototype.some method in JavaScript.
80. What are the differences between null, undefined, and undeclared in JavaScript?
81. How can you capitalize the first letter of a string in JavaScript?
82. Explain the purpose of the Array.prototype.every method in JavaScript.
83. What are the differences between let, const, and var in JavaScript?
84. How can you remove falsy values from an array in JavaScript?
85. Explain the purpose of the Array.prototype.slice method in JavaScript.
86. What are the differences between == and === operators in JavaScript?
87. How can you flatten an array in JavaScript?
88. Explain the purpose of the Array.prototype.sort method in JavaScript.
89. What are the differences between null, undefined, and undeclared in JavaScript?
90. How can you shuffle an array in JavaScript?
91. Explain the purpose of the Array.prototype.reverse method in JavaScript.
92. What are the differences between let, const, and var in JavaScript?
93. How can you find the intersection of two arrays in JavaScript?
94. Explain the purpose of the Array.prototype.join method in JavaScript.
95. What are the differences between == and === operators in JavaScript?
96. How can you find the union of two arrays in JavaScript?
97. Explain the purpose of the Array.prototype.splice method in JavaScript.
98. What are the differences between null, undefined, and undeclared in JavaScript?
99. How can you create a random number between two numbers in JavaScript?
100. Explain the purpose of the Array.prototype.concat method in JavaScript.

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These questions cover a wide range of topics and are designed to help you solidify your understanding of JavaScript concepts. Make sure to practice answering them and understand the underlying principles to confidently tackle any JavaScript interview. Good luck!