TypeScript

JavaScript with types

TypeScript adds static typing to JavaScript, catching errors at compile time and enabling powerful tooling for large codebases.

Large-scale apps

React/Next.js

Node.js APIs

Libraries & SDKs

Time to learn: 1-2 months (after JS)

1Type Annotations

beginner

Add explicit types to variables, parameters and return values.

function greet(name: string): string {
  return `Hello, ${name}`;
}

const age: number = 25;
const tags: string[] = ["dev", "ts"];

2Interfaces vs Types

beginner

Both describe object shapes; interfaces can be extended/merged, types can form unions.

interface User {
  id: number;
  name: string;
}

type Status = "active" | "inactive";

const u: User = { id: 1, name: "Ada" };
const s: Status = "active";

3Generics

intermediate

Write functions and types that work over multiple types without losing type safety.

function first<T>(items: T[]): T | undefined {
  return items[0];
}

const n = first<number>([1, 2, 3]); // number | undefined
const s = first(["a", "b"]);        // string | undefined

4Utility Types

intermediate

Built-in helpers transform existing types — invaluable in real apps.

interface Todo { id: number; title: string; done: boolean; }

type TodoPreview = Pick<Todo, "id" | "title">;
type PartialTodo = Partial<Todo>;
type ReadonlyTodo = Readonly<Todo>;

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