Changing and adding object properties

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. const student = { name: 'Ava', age: 15 }; student.age = 16; What is student.age now?

A 16

B 15

2. Which line changes the age property of student to 16?

A student.age = 16;

B student.age == 16;

3. const student = { name: 'Liam' }; student.house = 'Blue'; What happens?

A A new house property is added to student

B An error is thrown because house did not exist

4. const pet = { name: 'Rex' }; console.log(pet.age); What is printed?

A An error message

B undefined

5. True or false: you can change a property of an object that was declared with const.

A False

B True

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1student.age = 16;		Aconsole.log(student.email); // undefined
2student.house = "Red";		Bstudent.points = 50;
3Reading a property that was never added gives undefined		CChanges the existing age property of student to 16
4Use dot notation and = to give an object a new property		DAdds a new house property to student if it was not there before
5student.age == 16;		E== compares values instead of assigning. It does not change age. Use a single = to assign.
6student = 16;		FThis assigns to the whole variable, not the age property. It should be student.age = 16;

Definitions

student.age = 16

Fill in the Blanks

Complete each line of code by filling in the missing parts.

let student = { name: "Ava", age: 15 }; student.age _ 16; console.log(student.age);

let student = { name: "Ava", age: 15 }; _______.age = 16; console.log(student.age);

let student = { name: "Ava" }; student.age = 16; console.log(student.___);

let student = { name: "Ava" }; console.log(student.age); // prints _________

let student = { name: "Ava", age: 15 }; student.age __ 1; // age is now 16

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A const student = { age = 15 };

B student.age = 16;

C console.log(student.age);

Question 2

A const pet = { name: 'Rex' };

B pet.age = 3;

C pet.age = 4;

D console.log(pet.Age);

Question 3

A const car = { speed: 0 };

B car.speed = 50;

C car.colour == 'red';

D console.log(car.colour);

Question 4

A const dog = { name, 'Max' };

B dog.age = 2;

C console.log(dog.age);

Question 5

A const book = { pages: 100 };

B book.pages = 120;

C book.title: 'Maps';

D console.log(book.title);

Answer Key

Changing and adding object properties

Section A: Quick Questions

A — 16

A — student.age = 16;

A — A new house property is added to student

B — undefined

B — True

Section B: Match the Pairs

student.age = 16; → Changes the existing age property of student to 16

student.house = "Red"; → Adds a new house property to student if it was not there before

Reading a property that was never added gives undefined → console.log(student.email); // undefined

Use dot notation and = to give an object a new property → student.points = 50;

student.age == 16; → == compares values instead of assigning. It does not change age. Use a single = to assign.

student = 16; → This assigns to the whole variable, not the age property. It should be student.age = 16;

Section C: Definitions

student.age = 16 — Assigning to object.property with = changes an existing property or adds a new one if it is not there yet. Reading a property that does not exist gives undefined.

Section D: Fill in the Blanks

let student = { name: "Ava", age: 15 };
student.age = 16;
console.log(student.age);

let student = { name: "Ava", age: 15 };
student.age = 16;
console.log(student.age);

let student = { name: "Ava" };
student.age = 16;
console.log(student.age);

let student = { name: "Ava" };
console.log(student.age);
// prints undefined

let student = { name: "Ava", age: 15 };
student.age += 1;
// age is now 16

Section E: Spot the Error

A — Inside an object literal, each property is written as name: value with a colon. It should be { age: 15 }. The = sign is only used when assigning with dot notation after the object exists.

D — Property names are case-sensitive. The property was added as age, so pet.Age does not exist and gives undefined. It should be pet.age.

C — A double == compares values; it does not add or change a property. Use a single = to assign: car.colour = 'red'; adds the new colour property.

A — A property name and its value are separated by a colon, not a comma. It should be { name: 'Max' }.

C — A colon is only used inside the curly braces of an object literal. To add a property afterwards, use assignment with =: book.title = 'Maps';