Accessing object properties in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Accessing nested object properties

What is the output of the following code?

Javascript

const user = { name: 'Alice', details: { age: 30, city: 'Paris' } };
console.log(user.details.city);

A "Paris"

B "city"

C undefined

D TypeError

💡 Hint

Think about how to access properties inside nested objects using dot notation.

The property 'city' is inside the 'details' object. Accessing user.details.city returns the string 'Paris'.

❓ Predict Output

intermediate

Accessing object properties with bracket notation

What will this code output?

Javascript

const obj = { 'first-name': 'John', age: 25 };
console.log(obj['first-name']);

A "first-name"

B undefined

C "John"

D SyntaxError

💡 Hint

Use bracket notation to access properties with special characters or hyphens.

Since 'first-name' contains a hyphen, it must be accessed with bracket notation. obj['first-name'] returns 'John'.

❓ Predict Output

advanced

Accessing properties with variables

What is the output of this code?

Javascript

const key = 'score';
const player = { name: 'Bob', score: 42 };
console.log(player[key]);

A "score"

B 42

C undefined

D ReferenceError

💡 Hint

When using a variable to access a property, use bracket notation.

player[key] accesses the property named 'score' because key holds the string 'score'. The value is 42.

❓ Predict Output

advanced

Optional chaining with object properties

What will this code output?

Javascript

const data = { user: { profile: { name: 'Eve' } } };
console.log(data.user?.profile?.age);

A "age"

B null

C TypeError

D undefined

💡 Hint

Optional chaining returns undefined if a property does not exist instead of throwing an error.

The property 'age' does not exist inside profile, so data.user?.profile?.age returns undefined safely.

❓ Predict Output

expert

Dynamic property access and computed property names

What is the output of this code?

Javascript

const prefix = 'user';
const id = 7;
const obj = { [`${prefix}${id}`]: 'active' };
console.log(obj.user7);

A "active"

B SyntaxError

C undefined

D TypeError

💡 Hint

Computed property names allow dynamic keys in object literals.

The key is computed as 'user7', so obj.user7 returns 'active'.