Extending classes with types in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to extend a class in TypeScript?

Extending a class means creating a new class that inherits properties and methods from an existing class. This helps reuse code and add new features.

beginner

How do you specify the type of a class property when extending a class?

You declare the property with its type in the class definition. When extending, you can keep the same type or specify a more specific type if needed.

beginner

What is the syntax to extend a class named <code>Animal</code> in TypeScript?

Use <code>class Dog extends Animal { }</code> to create a new class <code>Dog</code> that inherits from <code>Animal</code>.

intermediate

Can a subclass override a method from its superclass in TypeScript? How?

Yes, a subclass can provide its own version of a method by defining a method with the same name. This replaces the superclass method when called on the subclass instance.

intermediate

How do you call the constructor of a superclass inside a subclass in TypeScript?

Use the <code>super()</code> function inside the subclass constructor to call the superclass constructor and pass any required arguments.

What keyword is used to create a class that inherits from another class in TypeScript?

A inherits

B implements

C super

D extends

The keyword extends is used to create a subclass that inherits from a superclass.

How do you specify the type of a property in a TypeScript class?

A propertyName: type;

B propertyName = type;

C type propertyName;

D propertyName -> type;

In TypeScript, you specify a property type using propertyName: type; syntax.

Which method allows a subclass to use the constructor of its superclass?

A this()

B super()

C parent()

D base()

The super() function calls the superclass constructor inside the subclass constructor.

If a subclass defines a method with the same name as its superclass, what happens?

A The subclass method overrides the superclass method.

B Both methods run automatically.

C The superclass method is called instead.

D An error occurs.

The subclass method replaces the superclass method when called on subclass instances.

Can a subclass add new properties not present in the superclass?

A No, subclasses must have the same properties.

B Only if the superclass allows it.

C Yes, subclasses can add new properties.

D Only if the subclass is abstract.

Subclasses can add new properties and methods beyond what the superclass has.

Explain how extending classes works in TypeScript and why it is useful.

Think about how a new class can get features from an existing class.

Describe how to override a method in a subclass and how to call the superclass constructor.

Focus on how subclasses change behavior and initialize.