Core Javascript Interview Questions

We have tried to cover maximum javascript interview questions possible - For Freshers and Experienced UI Developers

Question 1. How will you create array in javscript and tell some operations with array?

Now we are creating array

var x = [1,2,3,5,6]; // declaring x
console.log(x); //output: [1, 2, 3, 5, 6]

How to use Loop for array

x.forEach(function(item,index){
 console.log(index,item) 
})  
 
  output :- 
   0 1 
   1 2
   2 3
   3 5
   4 6

Remove first element from array

 var first = x.shift() // [2,3,5,6]

Add element front of array

 var last = x.unshift(1) // [1,2,3,5,6]
 

Question 2. What is Classical Inheritance in javscript?

Question 3. What is difference between async and defer?

Question 4. How to stop default behaviour of event bubbling?

Question 5. What is event bubbling and capturing?

Question 6. What happens when localStorage is full?

Question 7. what is prototype in javascript and how do you use it?

Question 8. what is arrow function in javascript?

Question 9. what is difference between ES6 and Javascript?

Question 10. How to handle multiline string in javascript?

Question 11. How to sort this array and remove duplicate values?

Array Values

var x = [5,6,4,2,3,7,3,4,5,7,7,3,2,1]; // Answer ?

Question 12. What is difference between "undefined" and "null" and "empty?

Question 13. What is Template Literals in es6?

Question 14. What is Spread Operators in es6?

Question 15. Explain Promises in javscript?

Question 16. What is Generator in javscript?

Question 17. What is difference between "Let", "Var", "Const" ?

Question 18. What is Closure in javscript ?

Question 19. How to compare two objects in javscript?

Question 20. What is Currying function in javscript?

Question 21. What is Callback function in javscript?

Question 22. What is "Call", "Apply", "Bind" in javscript?

Question 23. What is Immediately Invoked Function (IIFE) in javscript?

Question 24. What is "AMD" in javscript?

Question 25. Explain Hoisting in javscript?

Question 26. What is Type Conversion in javscript?

Question 27. What is difference between async and sync?

Question 28. Explain Object Creation Patterns?

Question 29. What is difference between "==" and "==="?

Question 30. What is "this" in javscript?

Question 31. What is difference between window and document?

Question 32. What is difference between DOM and Virtual DOM?

Question 33. What is Memoization in javscript?

Question 33. How to setTimeout in Ajax Call?

Question 34. How can we call multiple ajax call in one time?

Question 35. what will be Output?

var x = 1+"1"+"1" // console.log(x)

var x = 1-"1"+"2" // console.log(x)

var x = +1-"1"+"1" // console.log(x)

var x = 1+ +"1"+"2" // console.log(x)

var x = "2"-"1"+"1" // console.log(x)

Question 36. Reverse String in javscript?

Var x = "TestJavascript";

Question 37. Reverse a string in javscript?

Var x = "TestJavascript"; //Output ?

Question 37. Reverse a string in javscript?

Var x = "TestJavascript"; //Output ?