Accessing object properties in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the value of the 'name' property from the object.

Javascript

const person = { name: 'Alice', age: 25 };
console.log(person.[1]);

Drag options to blanks, or click blank then click option'

Aage

Bperson

Cname

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong property name.

Trying to access the object itself instead of its property.

To access the 'name' property of the object, use dot notation with 'name'.

2fill in blank

medium

Complete the code to access the 'age' property using bracket notation.

Javascript

const person = { name: 'Bob', age: 30 };
console.log(person[[1]]);

Drag options to blanks, or click blank then click option'

Aname

B'name'

Cage

D'age'

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the property name.

Using the wrong property name.

Bracket notation requires the property name as a string inside quotes.

3fill in blank

hard

Fix the error in accessing the 'city' property from the object.

Javascript

const location = { city: 'Paris', country: 'France' };
console.log(location[1]);

Drag options to blanks, or click blank then click option'

A['city']

B.city()

C.city

Dcity

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses like a function call.

Omitting quotes in bracket notation.

To access a property with bracket notation, use brackets and quotes: ['city'].

4fill in blank

hard

Fill both blanks to create an object with a property and access it using bracket notation.

Javascript

const obj = { [1]: 100 };
console.log(obj[[2]]);

Drag options to blanks, or click blank then click option'

A'score'

C'points'

Attempts:

3 left

💡 Hint

Common Mistakes

Using different property names in object and access.

Omitting quotes around property names.

The property name must be the same string in the object and when accessed with brackets.

5fill in blank

hard

Fill all three blanks to create an object and access a nested property.

Javascript

const data = { user: { [1]: 'John' } };
const key = [2];
console.log(data.user[[3]]);

Drag options to blanks, or click blank then click option'

A'firstName'

Ckey

D'lastName'

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation with a variable instead of bracket notation.

Mismatching property names.

The nested property is 'firstName', stored in variable 'key', used to access the property.

Practice

1. Which notation is used to access a property named age in a JavaScript object person when the property name is known and simple?

easy

A. person->age

B. person.age

C. person['age']

D. person(age)

Solution

1. Step 1: Understand dot notation usage

   Dot notation is used when the property name is a simple, valid identifier known in advance.

2. Step 2: Apply dot notation to access property

   Using person.age accesses the age property directly.

3. Final Answer:

   person.age -> Option B

4. Quick Check:

   Dot notation = person.age [OK]

Hint: Use dot notation for simple known property names [OK]

Common Mistakes:

• Using arrow (->) instead of dot
• Using parentheses like a function call
• Using bracket notation unnecessarily

2. Which of the following is the correct syntax to access the property "first-name" of an object user?

easy

A. user['first-name']

B. user.first-name

C. user.first_name

D. user[first-name]

Solution

1. Step 1: Identify property name with special characters

   The property name "first-name" contains a hyphen, which is not valid for dot notation.

2. Step 2: Use bracket notation with quotes

   Bracket notation with quotes, user['first-name'], correctly accesses such properties.

3. Final Answer:

   user['first-name'] -> Option A

4. Quick Check:

   Bracket notation for special chars = user['first-name'] [OK]

Hint: Use bracket notation for property names with special characters [OK]

Common Mistakes:

• Using dot notation with hyphenated names
• Omitting quotes inside brackets
• Using undefined variable inside brackets

3. What will be the output of the following code?

const car = { brand: 'Toyota', year: 2020 };
console.log(car['brand']);

medium

A. Error

B. brand

C. undefined

D. Toyota

Solution

1. Step 1: Understand bracket notation access

   The code uses bracket notation with the string 'brand' to access the property value.

2. Step 2: Retrieve the value of 'brand'

   The value of car['brand'] is 'Toyota', so it prints 'Toyota'.

3. Final Answer:

   Toyota -> Option D

4. Quick Check:

   car['brand'] = 'Toyota' [OK]

Hint: Bracket notation with string key returns property value [OK]

Common Mistakes:

• Confusing property name with value
• Expecting property name to print
• Using wrong quotes causing error

4. Identify the error in the following code snippet:

const book = { title: '1984', author: 'Orwell' };
console.log(book[title]);

medium

A. Syntax error due to missing semicolon

B. Dot notation should be used instead

C. Missing quotes around 'title' in bracket notation

D. Property 'title' does not exist

Solution

1. Step 1: Check bracket notation usage

   Inside brackets, property names must be strings or variables. Here, title is treated as a variable, not a string.

2. Step 2: Fix by adding quotes

   Adding quotes: book['title'] correctly accesses the property.

3. Final Answer:

   Missing quotes around 'title' in bracket notation -> Option C

4. Quick Check:

   Bracket keys need quotes if not variables [OK]

Hint: Put quotes around property names in brackets unless variable [OK]

Common Mistakes:

• Forgetting quotes around string keys
• Assuming dot notation always required
• Confusing variable and string keys

5. Given the object settings = { 'theme-color': 'dark', fontSize: 14 }, which code correctly changes the theme-color to 'light' and increases fontSize by 2?

hard

A. settings['theme-color'] = 'light'; settings.fontSize += 2;

B. settings.theme-color = 'light'; settings['fontSize'] += 2;

C. settings.theme-color = 'light'; settings.fontSize = settings.fontSize + 2;

D. settings['theme-color'] = 'light'; settings['fontSize'] =+ 2;

Solution

1. Step 1: Update 'theme-color' using bracket notation

   Since 'theme-color' has a hyphen, use bracket notation: settings['theme-color'] = 'light';

2. Step 2: Increase fontSize using dot notation

   fontSize is a simple property, so settings.fontSize += 2; correctly adds 2.

3. Final Answer:

   settings['theme-color'] = 'light'; settings.fontSize += 2; -> Option A

4. Quick Check:

   Bracket for special keys + dot for simple keys [OK]

Hint: Use bracket for special keys, dot for simple keys [OK]

Common Mistakes:

• Using dot notation for hyphenated keys
• Mistyping += as =+
• Mixing up property names and strings