JS Practice Questions
Topics Covered:
JS Variables, Data Types, Functions, Classes, Loops, Promises, ES6 Features, and more
30 Questions
Practice Questions
1. Which keyword is used to declare a variable that is function-scoped in JavaScript?
2. What is the difference between == and === in JavaScript?
3. Which method converts a JSON string into a JavaScript object?
4. What is the output of
console.log(typeof NaN); in JavaScript?
5. What does the
this keyword refer to in JavaScript (in a non-strict function context)?
6. What is an arrow function in JavaScript?
7. Which array method is used to execute a function on each element without creating a new array?
8. Which method adds one or more elements to the end of an array?
9. What does the
push() method return when called on an array?
10. What is a promise in JavaScript?
11. Which method is used to handle asynchronous operations after a promise is fulfilled?
12. What does the
fetch() API do in JavaScript?
13. How do you declare a constant variable in JavaScript?
14. Which method removes the last element from an array in JavaScript?
15. What will be the output of
console.log(0.1 + 0.2 === 0.3); in JavaScript?
16. Which of the following is a valid way to declare an arrow function in JavaScript?
const add = (a, b) => a + b;
17. Which method creates a new array with the results of calling a provided function on every element?
18. What is the output of
console.log(typeof []); in JavaScript?
19. Which function converts a string to an integer in JavaScript?
20. What is the difference between
null and undefined in JavaScript?
21. Which function is used to schedule a function to run after a specified delay?
22. Which of the following is a feature introduced in ES6?
23. What does destructuring in JavaScript allow you to do?
24. What is the purpose of the spread operator (
...) in JavaScript?
25. Which method returns a new array containing all elements that pass a test in JavaScript?
26. What is a closure in JavaScript?
27. Which keyword is used to import modules in ES6 JavaScript?
28. What does the
async keyword do in JavaScript?
29. Which method converts a JavaScript object into a JSON string?
30. Which method is used to add an element at the beginning of an array in JavaScript?
