JavaScript Interview Questions


Javascript is an interpreted programming language. It is mainly used for the development of network-centric applications. It is a lightweight language and integrated with java.

Moreover, it is integrated with HTML also, which makes its implementation easy. Javascript usage has now extended to mobile App development [in the form of React Native, etc.], Desktop app development [in the form of ReactJs, etc.], and Game Development[in the form of BabylonJs, etc.].

This article will provide you with all types of interview questions in the placement rounds of various reputed companies. You will find tons of questions to learn any programming language, not only Javascript; you just need to code, and code, and finally code until you become an expert.

Basic Level Interview Questions

  1. What is Javascript?
  2. List some features of Javascript.
  3. What name was given to Javascript in the initial days?
  4. List some advantages of Javascript.
  5. List some disadvantages of Javascript.
  6. Explain the named function in Javascript.
  7. What are the types of functions in Javascript?
  8. Explain the anonymous function.
  9. Is it possible to assign an anonymous function to a variable?
  10. Explain the argument object in Javascript.
  11. Define closure.
  12. Which method is used to return the character from a specific index?
  13. Explain the difference between Javascript and Jscript.
  14. How will you write a simple ‘Hello World’ in Javascript?
  15. How will you differentiate between Java and Javascript?
  16. How will you write normal text code dynamically?
  17. What type of scripting language is Javascript?
  18. Define null value in Javascript.
  19. How will you run the Javascript code on the server?
  20. Are Javascript objects class-based or prototype-based?
  21. Does Javascript support multithreading?
  22. How will Javascript achieve concurrency?
  23. How to use an external Javascript file?
  24. Is Javascript a case-sensitive language?
  25. Explain Browser Object Model.
  26. What do you know about DOM?
  27. Explain the use of document objects.
  28. Explain the use of window objects.
  29. What is the use of historical objects?
  30. How will you write a comment in Javascript?
  31. How to create a function in Javascript?
  32. Name the different data types present in Javascript.
  33. Explain the difference between == and ===?
  34. How will you write HTML code dynamically using Javascript?
  35. How to create objects in Javascript?
  36. What are the different ways of creating an array in Javascript?
  37. For what isNaN() function is used for?
  38. Tell me the output of 10+20+ “50” in Javascript.
  39. Tell me the output of “50”+10+20 in Javascript.
  40. Highlight the differences between Client-side Javascript and Server side Javascript.
  41. Where do cookies are stored on the hard disk?
  42. Explain the difference between event.preventDefault(), and event.stopPropagation() methods in Javascript?
  43. Explain undefined values in Javascript.
  44. How will you set the cursor to wait in Javascript?
  45. What is [[[ ]]]?
  46. Do you think Java and Javascript are the same or not?
  47. Explain negative infinity.
  48. Differentiate between View state and Session state.
  49. Name the various pop-up boxes available in Javascript.
  50. How will you detect the Operating System of the client machine using Javascript?

Advanced Level Interview Questions

  1. Explain hosting in Javascript.
  2. What do you understand by Implicit Type Coercion in Javascript?
  3. Is Javascript a statically typed or a dynamically typed language?
  4. Define NaN property in Javascript.
  5. Explain passed by value and passed by reference.
  6. What is the use of a Date object in Javascript?
  7. What is the role of set objects in Javascript?
  8. Define Immediately Invoked Function in Javascript.
  9. Define Higher order functions in Javascript.
  10. Explain the working of the “this” keyword.
  11. Explain bind(), call(), and apply() methods?
  12. What do you understand by the term Currying in Javascript?
  13. Define scope and scope chain in Javascript.
  14. Define object prototypes.
  15. What are callbacks?
  16. What is memorization?
  17. Define recursion in a programming language.
  18. Explain the use of a constructor function in Javascript.
  19. What are arrow functions?
  20. What is the difference between declaring variables using var, let, and const?
  21. What are the rest operator and spread operator?
  22. Explain the uses of promises in Javascript.
  23. Explain classes in Javascript.
  24. What are generator functions?
  25. Explain weekset in Javascript.
  26. Explain object Destructuring?
  27. Explain Temporal Dead Zone?
  28. What are falsy values in Javascript?
  29. How will you identify whether a value is false or not?
  30. Explain the use of the week map object in Javascript.
  31. What is a WeakSet object in Javascript?
  32. Explain the use of the TypedArray object in Javascript.
  33. For what function is the Boolean object used in Javascript?
  34. Explain the use of a Number object in Javascript.
  35. Explain the use of Math objects in Javascript.
  36. Explain the role of strict mode in Javascript.
  37. Explain the use of the debugger keyword in Javascript.
  38. What is the requirement of debugging in Javascript?
  39. How will you validate an email in Javascript?
  40. How to validate a form in Javascript?
  41. Do you think Javascript is faster than ASP script or not?
  42. What will be your approach to calculating the the Fibonacci series in Javascript?
  43. Explain number objects in Javascript.
  44. What are escape characters in Javascript?
  45. Explain the difference between escape() and unescaped() functions?
  46. Explain screen objects. State their properties.
  47. What role do deferred scripts play in Javascript?
  48. Write down the syntax of the for-in loop in Javascript.
  49. What are the different ways of creating an array in Javascript?
  50. Explain Event Bubbling and Event Capturing.


  • Barry Allen

    A Full Stack Developer with 10+ years of experience in different domain including SAP, Blockchain, AI and Web Development.


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