Web Development JavaScript 3

Question 1

What is the purpose of the `Promise.all()` method?

Accepted Answer

Resolves when all promises resolve, or rejects if any one rejects

Answer

`Promise.all()` takes an iterable of promises and returns a single promise that resolves with an array of results when all input promises resolve.

Question 2

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

Accepted Answer

Expands the array elements into individual arguments or elements

Answer

The spread operator expands an iterable like an array into individual elements, useful for function calls or array literals.

Question 3

Which event fires when the DOM is fully loaded but before images and stylesheets have loaded?

Accepted Answer

DOMContentLoaded

Answer

`DOMContentLoaded` fires when the initial HTML is parsed and DOM is ready, without waiting for stylesheets, images, or subframes.

Question 4

What is the result of `typeof undefined`?

Accepted Answer

'undefined'

Answer

`typeof undefined` returns the string `'undefined'`, which is one of the few safe uses of `typeof` with uninitialized values.

Question 5

How do you prevent an object's properties from being modified in JavaScript?

Accepted Answer

Object.freeze()

Answer

`Object.freeze()` prevents adding, removing, or modifying properties on an object.

Web Development Practice Test