Typed Classes

TypeScript classes help us model real-world entities with precise fields, typed behavior, and controlled access. If you’re coming from JavaScript, this removes the uncertainty of runtime design. If you’re already thinking in types, this brings structure and safety to your models.

By the end of this lesson, we'll be writing classes that are structured, type-safe, and ready for real-world use.

Why classes—and why TypeScript makes them better

In JavaScript, classes are flexible, but that flexibility cuts both ways. We can forget to initialize a property. Mistype a method parameter. Accidentally expose internal state. And we won’t find out until runtime—if we’re lucky.

TypeScript closes those gaps. With strict mode enabled, which we’ve done throughout this course, we get guarantees that make our class designs safer, clearer, and more robust:

• TypeScript helps ensure fields are initialized at compile time, either inline or in the constructor, reducing the risk of half-formed objects.

• Methods are fully type checked—we get immediate feedback if parameters are wrong or return values don’t match expectations.

• Access modifiers give us precise control—we define what’s exposed and what’s internal, making our APIs harder to misuse.

• Constructors are type-checked at compile time, so calls must match the declared parameter list and types.

This isn’t only about safety—it’s also about clarity. It ensures that the structure we define is the structure we get, consistently and reliably.

Defining a class with typed fields

We’ve all worked with classes in JavaScript. TypeScript builds on that familiar foundation by adding explicit types, guaranteed initialization, and strict enforcement of method contracts.

We declare fields with clear types. We use constructors to ensure proper setup. And we define methods with fully typed inputs and return values—giving us predictable, verifiable behavior from the start.

Let’s walk through a complete example.