javascriptbeginner

JavaScript Basics Quiz

Variables, types, operators, functions, and core JavaScript concepts.

7 questions

By EZ4Code TeamLast updated: 2026-08-01

1. Which keyword declares a block-scoped variable that CANNOT be reassigned?

var

let

const

static

Explanation: `const` declares a block-scoped variable that cannot be reassigned. `let` is block-scoped but reassignable. `var` is function-scoped and reassignable. `static` is not a JavaScript variable keyword.

2. What does `typeof null` return in JavaScript?

console.log(typeof null);

"null"

"object"

"undefined"

"number"

Explanation: This is a famous JavaScript quirk: `typeof null` returns `"object"`. It's a legacy bug from the original implementation that can't be fixed without breaking existing code. To check for null, use `value === null`.

3. What is the output?

console.log(0.1 + 0.2 === 0.3);

true

false

Error

undefined

Explanation: Floating-point math in JavaScript (IEEE 754) gives `0.1 + 0.2 = 0.30000000000000004`, not exactly `0.3`. So the strict equality check returns `false`. Use `Math.abs(a - b) < Number.EPSILON` for float comparison.

4. Which method adds an element to the END of an array?

push()

pop()

shift()

unshift()

Explanation: `push()` adds to the end. `pop()` removes from the end. `shift()` removes from the beginning. `unshift()` adds to the beginning.

5. What does `"5" + 3` evaluate to?

console.log("5" + 3);

"53"

53 (number)

NaN

Explanation: When you use `+` with a string, JavaScript coerces the other operand to a string and concatenates. So `"5" + 3` becomes `"53"` (a string). Note: `"5" - 3` would give `2` because `-` triggers numeric coercion.

6. Which operator checks both value AND type?

===

Explanation: `===` is strict equality — it checks both value and type without coercion. `==` is loose equality and performs type coercion (e.g. `"5" == 5` is `true`). `=` is assignment, not comparison.

7. What does `console.log(typeof undefined)` print?

"undefined"

"null"

"object"

"string"

Explanation: `typeof undefined` returns the string `"undefined"`. This is the correct, expected behavior (unlike `typeof null` which returns `"object"` due to a legacy bug).