JavaScript Object Methods

Question 1

What does `Object.keys()` return?

Accepted Answer

An array of an object's own enumerable property names

Answer

`Object.keys()` returns an array of a given object's own enumerable string property names (keys). It does not include inherited properties or non-enumerable properties.

Question 2

What does `Object.assign()` do?

Accepted Answer

Copies all enumerable own properties from one or more source objects to a target object

Answer

`Object.assign(target, ...sources)` copies all enumerable own properties from source objects into the target object. It returns the target. This is a shallow copy — nested objects are referenced, not cloned.

Question 3

What does `Object.freeze()` do?

Accepted Answer

Prevents all modifications — adding, deleting, or changing property values

Answer

`Object.freeze()` prevents new properties from being added, existing properties from being removed, and existing property values from being changed. It makes the object effectively immutable (shallowly).

Question 4

What does `Object.entries()` return?

Accepted Answer

An array of [key, value] pairs for own enumerable properties

Answer

`Object.entries()` returns an array of a given object's own enumerable string-keyed property `[key, value]` pairs. It's useful for iterating over objects with both key and value.

Question 5

What is the difference between `Object.seal()` and `Object.freeze()`?

Accepted Answer

`seal()` prevents adding/deleting properties but allows changing existing values; `freeze()` prevents all changes

Answer

`Object.seal()` prevents adding new properties and deleting existing ones, but allows changing the values of existing properties. `Object.freeze()` additionally prevents changing existing property values.

JavaScript Practice Test

JavaScript Practice Test

JavaScript Object Methods