Difference Between implements and extends in TypeScript

Understanding implements vs. extends helps you choose the right composition pattern in TypeScript.

Definitions

implements

“Implement” a contract. A class implements an interface (or another class) by providing all required members. It can override methods/properties and add new ones.

extends

“Inherit” behavior. A class or interface extends another class/interface, inheriting members. Properties are inherited; methods can be overridden.

Key Rules in TypeScript

1. Only classes use implements (classes can implement interfaces or classes).
2. Interfaces can extend interfaces or classes.
3. Classes can only extend classes (not interfaces).
4. Multiple inheritance/implementation is allowed.

Java Comparison

In Java:

1. Same as TypeScript: classes implement interfaces and extend classes. Multiple inheritance via interfaces is allowed.
2. Difference: interfaces can’t extend classes—only other interfaces.

Takeaway

This is just a starting point; real-world use comes from practice.

References

• What’s the difference between ’extends’ and ‘implements’ in TypeScript
• Implements vs extends: When to use? What’s the difference?
• Object-oriented programming (Wikipedia)
• Classes & Interfaces in TypeScript