Nested objects in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested object in JavaScript?

A nested object is an object that is a value inside another object. It means one object contains another object as a property.

beginner

How do you access a property inside a nested object?

You use dot notation or bracket notation for each level. For example, obj.innerObj.property accesses property inside innerObj which is inside obj.

beginner

Given <code>const person = { name: 'Anna', address: { city: 'Paris', zip: 75000 } };</code>, how do you get the city?

You get the city by writing person.address.city. This goes inside the address object to get the city property.

intermediate

Can nested objects contain arrays or other nested objects?

Yes! Nested objects can have arrays or even more objects inside them. This lets you build complex data structures.

intermediate

How do you safely access a deeply nested property without errors if some parts might be missing?

You can use optional chaining like obj?.innerObj?.property. This stops and returns undefined if any part is missing, avoiding errors.

What does the following code access?<br>user.profile.email

A The user property inside the profile object of email

B The profile property inside the email object of user

C The email property inside the profile object of user

D The profile property inside the user object called email

Dot notation reads from left to right: user → profile → email property.

Which is the correct way to access the zip code in this object?<br>const data = { location: { zip: 12345 } };

A data.zip

B data.location.zip

C data['zip']

D data.location['city']

The zip code is inside the location object, so use data.location.zip.

What will obj?.inner?.value return if obj.inner is undefined?

A Returns false

B Throws an error

C Returns null

D Returns undefined

Optional chaining returns undefined if any part before it is missing, avoiding errors.

Can a nested object property be an array?

A Yes, objects can contain arrays as properties

B No, objects can only contain other objects

C Only if the array has objects inside

D Only if the array is empty

Objects can have any type as property values, including arrays.

How do you add a new nested object property to an existing object?

A Use dot notation to assign a new object, e.g., obj.newProp = {}

B You cannot add nested properties after creation

C Use array methods

D Use JSON.stringify

You can add nested properties anytime by assigning an object to a property.

Explain what a nested object is and how you access its properties in JavaScript.

Think about objects inside objects and how to reach inside.

Describe how optional chaining helps when working with nested objects.

It uses question marks to safely check each level.