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Javascript interview questions

As an Angular professional, it is essential to know the Javascript, learn the right technologies and prepare the right answers to commonly asked Javascript Interview Questions. Here’s a definitive list of top 40 Javascript Interview Questions.


Basic Javascript Questions 

Question 1. What are JavaScript Data Types? Question 2. What is the use of isNaN function? Question 3. What are undeclared and undefined variables? Question 4. Write the code for adding new elements dynamically? Question 5. What is ‘this’ keyword in JavaScript? Question 6. What is === operator? Question 7. Explain how can you submit a form using JavaScript? Question 8. Does JavaScript support automatic type conversion? Question 9. Explain the difference between “==” and “===”? Question 10. What would be the result of 6+2+”1"? Question 11.Explain how to detect the operating system on the client machine? Question 12. What do mean by NULL in Javascript? Question 13. What is the function of delete operator? Question 14. What is an undefined value in JavaScript? Question 15. What are JavaScript Cookies? Question 16. Explain what is pop()method in JavaScript? Question 17. What is the use of Push method in JavaScript? Question 18. What is unshift method in JavaScript? Question 19. Mention what is the disadvantage of using innerHTML in JavaScript? Question 20. Which keywords are used to handle exceptions? Question 21. What are the different types of errors in JavaScript? Question 22. What is the ‘Strict’ mode in JavaScript and how can it be enabled? Question 23. Explain window.onload and onDocumentReady? Question 24. What is the difference between .call() and .apply()? Question 25. Describe the properties of an anonymous function in JavaScript? Question 26. Define event bubbling? Question 27. What is the method for reading and writing a file in JavaScript? Question 28. How are DOM utilized in JavaScript?

Medium Javascript Questions

Question 29. What is a “closure” in JavaScript? Provide an example. Question 30. Difference between “var” and “let” Keywords? Question 31. What is prototypal Inheritance? Question 33. What is SetTimeout()? Question 34. What is Scope? Question 35. What is ECMAScript? Question 36. What are Template Literals? Question 37. What are Promises? Question 38. What is AJAX? And explain it with usage? Question 39. What’s the difference between the in operator and the hasOwnProperty method in objects? Question 40. What are the ways to deal with Asynchronous Code in JavasScript? Question 41. How to evaluate multiple expressions in one line?

I hope these set of questions would help you to prepare for Javascript interview.

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