JavaScript Quiz

Question 1

What does `typeof null` evaluate to in JavaScript?

Accepted Answer

"object"

Answer

"null"

Answer

"undefined"

Answer

"boolean"

Question 2

What is the result of `0.1 + 0.2 === 0.3`?

Accepted Answer

false

Answer

true

Answer

NaN

Answer

throws an error

Question 3

Which statement about `let` and `const` is correct?

Accepted Answer

They are block-scoped and hoisted but not initialized (temporal dead zone)

Answer

They are function-scoped like `var`

Answer

They cannot be hoisted at all

Answer

`const` variables can never hold an object that is later mutated

Question 4

What will `console.log(a)` print? `var a = 1; function f() { console.log(a); var a = 2; } f()`

Accepted Answer

undefined

Answer

1

Answer

2

Answer

ReferenceError

Question 5

A closure is best described as…

Accepted Answer

A function bundled with references to its surrounding lexical scope

Answer

A block of code that runs immediately

Answer

An object with private methods

Answer

A way to close a database connection

Question 6

In the event loop, which queue is drained first after the current task?

Accepted Answer

The microtask (Promise) queue

Answer

The macrotask (setTimeout) queue

Answer

They alternate strictly one-for-one

Answer

Rendering always runs first

Question 7

What does `[1, 2, 3].map(parseInt)` return?

Accepted Answer

[1, NaN, NaN]

Answer

[1, 2, 3]

Answer

[1, 2, 3] as strings

Answer

[NaN, NaN, NaN]

Question 8

How does `==` differ from `===`?

Accepted Answer

`==` performs type coercion, `===` does not

Answer

They are identical

Answer

`==` compares by reference, `===` by value

Answer

`===` is slower and deprecated

Question 9

What is the value of `this` inside a regular function called as `obj.method()`?

Accepted Answer

The `obj` receiver

Answer

The global object

Answer

`undefined`

Answer

The function itself

Question 10

Which method creates a new array with only elements that pass a test?

Accepted Answer

filter()

Answer

map()

Answer

forEach()

Answer

reduce()

JavaScript quiz

What does `typeof null` evaluate to in JavaScript?

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