Class property declarations in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a class property declaration in TypeScript?

A class property declaration defines a variable inside a class to hold data for each object created from that class. It sets the name and type of the property.

beginner

How do you declare a public property named name of type string in a TypeScript class?

You write: <pre>class Person {
  public name: string;
}</pre> This means every Person object has a <code>name</code> property that holds a string.

intermediate

What is the difference between declaring a property with and without an access modifier in TypeScript?

If you declare a property without an access modifier, it is public by default. Using private or protected changes who can access the property.

beginner

Can you assign a default value to a class property in its declaration? Show an example.

Yes. You can assign a default value like this:<pre>class Car {
  color: string = "red";
}</pre> Every new Car object will have <code>color</code> set to "red" unless changed.

intermediate

What happens if you declare a property but do not initialize it in the class or constructor?

The property exists but is undefined until you assign a value. TypeScript may warn if you don't initialize or mark it optional.

Which keyword declares a property that can only be accessed inside the class?

A private

B public

C protected

D readonly

The private keyword restricts access to the property only within the class.

What is the default access level of a class property if no modifier is specified?

A private

B protected

C public

D readonly

Properties are public by default, meaning accessible anywhere.

How do you assign a default value to a class property in TypeScript?

A Using an equals sign in the property declaration

B Inside the constructor only

C Using a method

D You cannot assign default values

You assign default values directly in the property declaration with an equals sign.

Which of these is a valid property declaration in TypeScript?

A const age: number;

B let age: number;

C var age: number;

D age: number;

Inside a class, properties are declared without let, var, or const keywords.

What does the readonly modifier do when used with a class property?

A Makes the property private

B Prevents the property from being changed after initialization

C Allows the property to be changed anywhere

D Makes the property optional

readonly means the property can only be assigned once, usually at declaration or in the constructor.

Explain how to declare and initialize a class property with a default value in TypeScript.

Think about using an equals sign in the property line.

Describe the difference between public, private, and protected class properties in TypeScript.

Consider who can see or change the property.