JavaScript Object Methods 2

Question 1

What does `Object.fromEntries()` do?

Accepted Answer

Creates an object from an iterable of key-value pairs

Answer

`Object.fromEntries()` transforms a list of key-value pairs (such as from `Object.entries()`, a Map, or any iterable of `[key, value]`) into an object.

Question 2

How does the `for...in` loop differ from `for...of` when used with objects?

Accepted Answer

`for...in` iterates over enumerable property names; `for...of` requires an iterable and plain objects are not iterable

Answer

`for...in` iterates over all enumerable string property names, including inherited ones. `for...of` works only on iterables (arrays, Sets, Maps, strings); plain objects are not iterable by default.

Question 3

What is property shorthand in ES6 object literals?

Accepted Answer

Omitting the value when variable name matches the property name

Answer

Property shorthand allows you to omit the value when the property name matches a variable in scope: instead of `{ name: name, age: age }`, you can write `{ name, age }`.

Question 4

What are computed property names in JavaScript objects?

Accepted Answer

Property names defined using expressions inside square brackets

Answer

Computed property names allow you to use an expression inside square brackets as a property name in an object literal: `{ [expr]: value }`. The expression is evaluated at runtime to determine the key.

Question 5

What is the purpose of `Object.getPrototypeOf()`?

Accepted Answer

Returns the prototype (internal `[[Prototype]]`) of the specified object

Answer

`Object.getPrototypeOf(obj)` returns the prototype of the specified object — the value of the internal `[[Prototype]]` property. It's the standard way to get the prototype chain.

JavaScript Practice Test

JavaScript Practice Test

JavaScript Object Methods 2