Reading and changing an object's properties

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Dog class: const rex = new Dog('Rex', 3). Which line reads Rex's age?

A console.log(Dog.age);

B console.log(rex.age);

2. Which line changes rex's age to 4?

A rex.age = 4;

B rex.age == 4;

3. rex.age is 3. After rex.age = 4; runs, what does console.log(rex.age) print?

A 4

B 3

4. const rex = new Dog('Rex', 3); const fido = new Dog('Fido', 5); rex.age = 4; What is fido.age?

A 4

B 5

5. Which is the correct way to read the name property of an object called fido?

A fido.name

B fido(name)

Match the Pairs

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

Left column		Right column
1rex.age		Aconsole.log(rex.name);
2rex.age = 4;		BReads the age property of the object stored in rex
3Print the value of a property stored in an object called rex		CBrackets are used instead of a dot. It should be rex.age to read the property.
4Changing one object's property does not change another object's copy		DChanges rex's age property to the new value 4
5rex.age == 4;		E== compares values instead of assigning. It should be rex.age = 4; to change the property.
6console.log(rex(age));		Frex.age = 4; console.log(milo.age);

Definitions

object.property

Fill in the Blanks

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

const rex = new Dog("Rex", 3); console.log(___.age);

const rex = new Dog("Rex", 3); rex.age _ 4; console.log(rex.age);

const rex = new Dog("Rex", 3); const mia = new Dog("Mia", 5); ___.age = 6; // rex.age is still 3

const rex = new Dog("Rex", 3); rex.age = rex.___ + 1; console.log(rex.age); // 4

const rex = new Dog("Rex", 3); rex.___ = 4; // Rex is now 4 years old console.log(rex.age);

Spot the Error

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

Question 1

A const rex = new Dog("Rex", 3);

B console.log(rex.Age);

C rex.age = 4;

Question 2

A const rex = new Dog("Rex", 3);

B console.log(rex.age);

C rex.age == 4;

D console.log(rex.age);

Question 3

A const mia = new Cat("Mia", 2);

B mia.age = age + 1;

C console.log(mia.age);

Question 4

A let rex = Dog("Rex", 3);

B let zed = new Dog("Zed", 5);

C rex.age = 4;

D console.log(zed.age);

Question 5

A let rex = new Dog("Rex", 3);

B let zed = new Dog("Zed", 5);

C rex.age = 4;

D console.log(zed.age());

Answer Key

Reading and changing an object's properties

Section A: Quick Questions

B — console.log(rex.age);

A — rex.age = 4;

A — 4

B — 5

A — fido.name

Section B: Match the Pairs

rex.age → Reads the age property of the object stored in rex

rex.age = 4; → Changes rex's age property to the new value 4

Print the value of a property stored in an object called rex → console.log(rex.name);

Changing one object's property does not change another object's copy → rex.age = 4; console.log(milo.age);

rex.age == 4; → == compares values instead of assigning. It should be rex.age = 4; to change the property.

console.log(rex(age)); → Brackets are used instead of a dot. It should be rex.age to read the property.

Section C: Definitions

object.property — Reads a property of an object, like rex.age. To change it, assign a new value: rex.age = 4. Each object keeps its own values.

Section D: Fill in the Blanks

const rex = new Dog("Rex", 3);
console.log(rex.age);

const rex = new Dog("Rex", 3);
rex.age = 4;
console.log(rex.age);

const rex = new Dog("Rex", 3);
const mia = new Dog("Mia", 5);
mia.age = 6; // rex.age is still 3

const rex = new Dog("Rex", 3);
rex.age = rex.age + 1;
console.log(rex.age); // 4

const rex = new Dog("Rex", 3);
rex.age = 4; // Rex is now 4 years old
console.log(rex.age);

Section E: Spot the Error

B — Property names are case-sensitive. rex.Age does not exist, so it prints undefined. It should be rex.age.

C — == compares two values and does not change anything. To change the property, use the assignment operator: rex.age = 4;

B — age on its own is not a variable, so this causes a ReferenceError. Read the property through the object: mia.age + 1.

A — An object is created from a class with the new keyword. It should be let rex = new Dog("Rex", 3);

D — age is a property, not a method, so it is read without brackets. zed.age() causes a TypeError. Use zed.age, which prints 5.