Multiple interface extension in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'multiple interface extension' mean in TypeScript?

It means one interface can inherit properties and methods from more than one other interface, combining them into a single interface.

beginner

How do you extend multiple interfaces in TypeScript? Show the syntax.

Use the extends keyword followed by a comma-separated list of interfaces. Example:<br>

interface A { a: number; }
interface B { b: string; }
interface C extends A, B { c: boolean; }

intermediate

Can a class implement an interface that extends multiple interfaces?

Yes. When a class implements such an interface, it must provide all properties and methods from all the extended interfaces.

advanced

What happens if two extended interfaces have properties with the same name but different types?

TypeScript will raise an error because the property types conflict. The extending interface must resolve the conflict or avoid incompatible overlaps.

beginner

Example: Write interfaces A and B, then interface C that extends both. Add one property to each. What properties does C have?

interface A { x: number; }
interface B { y: string; }
interface C extends A, B { z: boolean; }

<br>Interface C has properties x, y, and z.

How do you extend multiple interfaces in TypeScript?

A interface C extends A, B {}

B interface C implements A, B {}

C class C extends A, B {}

D class C implements A, B {}

Interfaces extend other interfaces using the 'extends' keyword with a comma-separated list.

If interface C extends interfaces A and B, which properties must a class implementing C have?

A Properties from A, B, and C

B Only properties from C

C Properties from A and B only

D No properties required

The class must implement all properties from A, B, and C.

What error occurs if two extended interfaces have the same property name but different types?

A No error, TypeScript merges types

B Type conflict error

C Runtime error only

D Property is ignored

TypeScript reports a type conflict error for incompatible property types.

Which keyword is used by a class to follow an interface?

A inherits

B extends

C implements

D uses

Classes use 'implements' to follow interfaces.

Can interfaces extend more than two interfaces?

A Only one interface allowed

B No, only two interfaces max

C Depends on TypeScript version

D Yes, any number separated by commas

Interfaces can extend any number of interfaces separated by commas.

Explain how multiple interface extension works in TypeScript and why it is useful.

Think about how you can combine different sets of properties into one interface.

Describe what happens when a class implements an interface that extends multiple interfaces.

Remember the class must fulfill all contracts from all interfaces.