Common JavaScript Interview Questions
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JavaScript Interview Questions
The most frequently asked JavaScript interview questions with concise answers.
1. var vs let vs const?
var is function-scoped; let and const are block-scoped. const can't be reassigned.
2. What is a closure?
A function that remembers variables from its outer scope even after that scope has returned. See our closures guide.
3. == vs ===?
0 == "0" // true (loose, type coercion)
0 === "0" // false (strict, no coercion)
// Always prefer ===4. What is hoisting?
Variable and function declarations are moved to the top of their scope before execution.
5. Explain "this"
this refers to the object calling the function — varies by context. Arrow functions inherit this.
6. What is the event loop?
The mechanism that handles async callbacks on JS's single thread.
7. Promise vs callback?
Promises avoid "callback hell" and support chaining and async/await.
8. What is destructuring?
const { name } = user;
const [first] = array;FAQs
How many questions to expect?
Usually 5-10 conceptual + coding problems. More in our interview prep and JS guides.
Should I memorize answers?
No — understand concepts so you can explain them naturally.