Can I use interfaces, classes, enums, and generics?

Yes. The examples demonstrate these features. Modify types and see compiler guidance.

Types and Unions with Narrowing

Practice unions and type narrowing to model flexible inputs safely. Learn how `typeof`, `in`, and control flow help the compiler refine types at runtime boundaries.

Try TypeScript Compiler

TypeScript: Union Types

Use union types to allow multiple types.

                          function formatId(id: number | string): string {
  return typeof id === "number" ? `#${id}` : id.toUpperCase();
}
console.log(formatId(42));
console.log(formatId("user-7"));
                        

Output

TypeScript: Type Narrowing

Narrow a union type with typeof and in.

                          type User = { id: number; name: string };
type Admin = User & { role: "admin" };
function greet(person: User | Admin) {
  if ("role" in person) {
    console.log(`Welcome admin ${person.name}`);
  } else {
    console.log(`Hello ${person.name}`);
  }
}
greet({ id: 1, name: "Sam" });
greet({ id: 2, name: "Jo", role: "admin" });
                        

Output

Keep Practicing

Use the online TypeScript compiler to run examples and test variations. Reinforce learning by building small scripts for each topic.

FAQ

No. This page transpiles TypeScript in the browser to run simple examples. For larger projects, use a local setup with a bundler.

Yes. The examples demonstrate these core TypeScript features. Try modifying types and observe how the compiler enforces correctness.

TypeScript transpiles to JavaScript, so runtime behavior matches JS. Type safety helps you catch errors before execution.

Learn TypeScript by Practicing Examples

Hands-on practice is the fastest way to understand TypeScript. Each example focuses on a single concept—from types, unions, and narrowing to interfaces, classes, generics, and enums. Modify examples, add new functions, and see how type checks guide your code.

Use our tools to deepen learning: the TypeScript Compiler to run snippets, and the TypeScript Tutorial for structured lessons.

Beginner-Friendly

Start with type annotations and unions, then learn narrowing and basic interfaces.

Practical Patterns

Practice classes, generics, enums, tuples, and utility types in small snippets.

Grow Skills

Explore async/await and type guards to build robust, readable code.

Types and Unions with Narrowing

TypeScript: Union Types

Output

TypeScript: Type Narrowing

Output

Keep Practicing

FAQ

Do I need Node or a build tool to try these examples?

Can I use interfaces, classes, enums, and generics?

Is the output identical to JavaScript?

Learn TypeScript by Practicing Examples

Beginner-Friendly

Practical Patterns

Grow Skills