JavaScript JavaScript 3

Question 1

What is a closure in JavaScript?

Accepted Answer

A function that has access to its outer scope's variables even after the outer function has returned

Answer

A closure is formed when an inner function retains access to variables from its enclosing scope even after that outer function has finished executing.

Question 2

What will `[1, 2, 3].indexOf(4)` return?

Accepted Answer

-1

Answer

`indexOf()` returns `-1` when the specified element is not found in the array.

Question 3

Which of the following is NOT a valid way to declare a variable in modern JavaScript?

Accepted Answer

def x = 1

Answer

`def` is not a JavaScript keyword; variables are declared with `var`, `let`, or `const`.

Question 4

What is the result of `typeof NaN` in JavaScript?

Accepted Answer

'number'

Answer

Despite standing for 'Not a Number', `NaN` is of type `'number'` in JavaScript.

Question 5

What does the spread operator (`...`) do when used with an array?

Accepted Answer

Expands the array's elements into individual values

Answer

The spread operator expands an iterable (like an array) into individual elements in places where multiple arguments or elements are expected.

JavaScript Practice Test

JavaScript Practice Test

JavaScript JavaScript 3