Class implementing multiple interfaces in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean for a class to implement multiple interfaces in TypeScript?

It means the class agrees to provide all the properties and methods defined in all the interfaces it implements. This helps ensure the class meets multiple contracts or behaviors.

beginner

How do you declare a class that implements two interfaces named <code>InterfaceA</code> and <code>InterfaceB</code>?

You write: <br><code>class MyClass implements InterfaceA, InterfaceB { /* implementation */ }</code>

intermediate

Can a class implement interfaces that have overlapping method names? What happens?

Yes, a class can implement interfaces with overlapping method names. The class must provide one implementation that satisfies all interfaces for that method.

intermediate

Why use multiple interfaces instead of a single big interface?

Using multiple smaller interfaces helps keep code organized and flexible. Classes can pick only the behaviors they need, making code easier to maintain and understand.

beginner

Example: What will this code output?<br><pre>interface A { greet(): void; }<br>interface B { farewell(): void; }<br>class Person implements A, B {<br>  greet() { console.log('Hello!'); }<br>  farewell() { console.log('Goodbye!'); }<br>}<br>const p = new Person();<br>p.greet();<br>p.farewell();</pre>

The output will be:<br><pre>Hello!<br>Goodbye!</pre><br>Because the class implements both interfaces and provides both methods.

How do you specify that a class implements multiple interfaces in TypeScript?

A List interfaces inside curly braces after the class name

B Separate interface names with commas after the 'implements' keyword

C Use the 'extends' keyword with multiple interfaces

D Use multiple 'implements' keywords, one per interface

In TypeScript, you list multiple interfaces separated by commas after the 'implements' keyword.

If two interfaces have a method with the same name but different return types, what happens when a class implements both?

A The class can implement only one interface's method

B TypeScript allows conflicting return types without error

C The compiler automatically merges the return types

D The class must provide a method compatible with both interfaces

The class must provide a method that satisfies both interfaces, so the method must be compatible with both return types.

Which of these is a benefit of implementing multiple interfaces?

A Allows a class to have multiple inheritance of implementation

B Automatically generates method implementations

C Enforces a class to follow multiple contracts or behaviors

D Prevents a class from having any methods

Implementing multiple interfaces enforces that a class follows multiple contracts or behaviors.

Can interfaces in TypeScript contain method implementations?

A No, interfaces only declare method signatures

B Yes, interfaces can have full method bodies

C Only if marked with 'default' keyword

D Only in classes, not interfaces

Interfaces only declare method signatures; they do not contain implementations.

What keyword is used to declare that a class follows an interface?

A implements

B extends

C uses

D inherits

The 'implements' keyword declares that a class follows an interface.

Explain how a class can implement multiple interfaces in TypeScript and why this is useful.

Think about how a class promises to have behaviors from more than one source.

Describe what happens if two interfaces have methods with the same name and a class implements both.

Consider how one method can fulfill multiple contracts.