JavaScript interview questions

Review short answers, detailed answers, practical code and common mistakes.

1. How would you explain JS Introduction in JavaScript during an interview?beginner

JS Introduction is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem js introduction solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "JS Introduction";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

2. How would you explain Variables in JavaScript during an interview?beginner

Variables is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem variables solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

3. How would you explain Data Types in JavaScript during an interview?beginner

Data Types is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem data types solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

4. How would you explain Operators in JavaScript during an interview?beginner

Operators is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem operators solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Operators";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

5. How would you explain Conditions in JavaScript during an interview?beginner

Conditions is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem conditions solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

6. How would you explain Loops in JavaScript during an interview?beginner

Loops is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem loops solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

7. How would you explain Functions in JavaScript during an interview?beginner

Functions is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem functions solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Functions";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

8. How would you explain Arrays in JavaScript during an interview?beginner

Arrays is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem arrays solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

9. How would you explain Objects in JavaScript during an interview?beginner

Objects is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem objects solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

10. How would you explain Strings in JavaScript during an interview?beginner

Strings is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem strings solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Strings";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

11. How would you explain DOM in JavaScript during an interview?intermediate

DOM is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem dom solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

12. How would you explain Events in JavaScript during an interview?intermediate

Events is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem events solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

13. How would you explain Forms in JavaScript during an interview?intermediate

Forms is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem forms solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Forms";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

14. How would you explain LocalStorage in JavaScript during an interview?intermediate

LocalStorage is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem localstorage solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

15. How would you explain Fetch API in JavaScript during an interview?intermediate

Fetch API is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem fetch api solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

16. How would you explain Promises in JavaScript during an interview?intermediate

Promises is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem promises solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

async function loadOrders() {
  const response = await fetch("/api/orders");
  if (!response.ok) throw new Error("Could not load orders");
  return response.json();
}

17. How would you explain Async/Await in JavaScript during an interview?intermediate

Async/Await is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem async/await solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

18. How would you explain Error Handling in JavaScript during an interview?intermediate

Error Handling is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem error handling solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

19. How would you explain Closures in JavaScript during an interview?intermediate

Closures is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem closures solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Closures";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

20. How would you explain Scope in JavaScript during an interview?intermediate

Scope is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem scope solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

21. How would you explain Hoisting in JavaScript during an interview?advanced

Hoisting is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem hoisting solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

22. How would you explain Event Loop in JavaScript during an interview?advanced

Event Loop is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem event loop solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const button = document.querySelector("#save");
button?.addEventListener("click", () => {
  document.body.dataset.saved = "true";
});

23. How would you explain Prototypes in JavaScript during an interview?advanced

Prototypes is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem prototypes solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

24. How would you explain Modules in JavaScript during an interview?advanced

Modules is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem modules solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

25. How would you explain Debounce and Throttle in JavaScript during an interview?advanced

Debounce and Throttle is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem debounce and throttle solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Debounce and Throttle";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

26. How would you explain OOP in JavaScript during an interview?advanced

OOP is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem oop solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

27. How would you explain Functional Programming in JavaScript during an interview?advanced

Functional Programming is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem functional programming solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

28. How would you explain Todo App Project in JavaScript during an interview?advanced

Todo App Project is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem todo app project solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

const lesson = "Todo App Project";
const checklist = ["understand", "run", "change", "explain"];
console.log(lesson + ": " + checklist.join(" -> "));

29. How would you explain Quiz App Project in JavaScript during an interview?advanced

Quiz App Project is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem quiz app project solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.

30. How would you explain JavaScript Review in JavaScript during an interview?advanced

JavaScript Review is best explained with its purpose, a small example, and one common mistake.

Start by naming the problem javascript review solves in JavaScript. Then show a short example, discuss the tradeoff, and mention how you would test it in a real codebase.