Prototypal Inheritance: Objects can inherit properties and methods from other objects using prototypes. Dynamic Structure: Objects can have properties added or removed dynamically. Flexibility: They can store mixed data types and methods (functions that belong to the object).

What are Objects?

Difficulty: 3/10

object literals, prototypes, property descriptors

In JavaScript, objects are one of the most fundamental and versatile data types. They are collections of key-value pairs, where the keys (also called properties) are strings or symbols , and the values can be of any data type, including other objects, functions, or arrays.

1
Prototypal Inheritance: Objects can inherit properties and methods from other objects using prototypes.
2
Dynamic Structure: Objects can have properties added or removed dynamically.
3
Flexibility: They can store mixed data types and methods (functions that belong to the object).

Scenario Questions

0-2 years experience

1You need to store a user's name, email, and a list of their favorite colors. Show me how you'd create that object and then add a new favorite color later.
2What happens if you try to read a property that doesn't exist on an object — say, user.age when age was never set? What if you then assign to it?
3Write a function that takes an object and a key, and returns true only if that key exists directly on the object (not inherited). How would you check that?

Follow-up Questions

How does property lookup work when a key isn't found on the object itself?
What's the difference between Object.create(null) and {}?
When would you use a Map instead of a plain object?