Why Merging classes with interfaces in Typescript? - Purpose & Use Cases

The Big Idea

Discover how to upgrade your classes without rewriting them and save hours of work!

The Scenario

Imagine you have a class that defines some behavior, and separately you want to add extra properties or methods to it without changing the original class code. Doing this manually means rewriting or duplicating code, which is confusing and error-prone.

The Problem

Manually copying or extending classes to add new features can lead to mistakes, duplicated code, and harder maintenance. It's like trying to add new features to a car by building a whole new car from scratch every time.

The Solution

Merging classes with interfaces lets you extend or add new properties to a class type without changing the original class code. It's like attaching new parts to your car easily without rebuilding it, keeping your code clean and flexible.

Before vs After

✗ Before

class Car { drive() { console.log('Driving'); } }
// To add new property, create a new class or duplicate code

✓ After

class Car { drive() { console.log('Driving'); } }
interface Car { color: string; }
// Now Car instances have color property without changing class

What It Enables

This concept enables you to enhance existing classes with new properties or methods seamlessly, making your code more adaptable and easier to maintain.

Real Life Example

Suppose you have a User class but later want to add an address property. Instead of rewriting the class, you merge an interface with the User class to add the address, keeping your original code untouched.

Key Takeaways

Merging classes with interfaces avoids code duplication.

It allows adding new features without changing original classes.

It keeps code clean, flexible, and easier to maintain.