developing-with-typescript

TypeScript Development Skill

TypeScript 5.x development with modern patterns including strict mode, generics, utility types, and modules.

Progressive Disclosure: Quick reference patterns here. See REFERENCE.md for advanced topics.

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When to Use

Loaded by backend-developer or frontend-developer when:

• tsconfig.json present in project
• package.json contains typescript dependency
• .ts or .tsx files in project

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Quick Start

Basic Types

// Primitives
const name: string = "Alice";
const age: number = 30;
const isActive: boolean = true;

// Arrays and Tuples
const numbers: number[] = [1, 2, 3];
const point: [number, number] = [10, 20];
const rest: [string, ...number[]] = ["scores", 1, 2, 3];

Interfaces vs Type Aliases

// Interfaces - object shapes, extensible, declaration merging
interface User {
  id: string;
  name: string;
  email: string;
}

interface Admin extends User {
  permissions: string[];
}

// Type aliases - unions, tuples, primitives, complex types
type ID = string | number;
type Point = [number, number];
type Callback = (data: string) => void;
type AdminUser = User & { permissions: string[] };

Functions

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

// Arrow with optional/default params
const createUser = (name: string, age?: number, role = "user") => ({ name, age, role });

// Function overloads
function parse(input: string): string[];
function parse(input: string[]): string;
function parse(input: string | string[]): string | string[] {
  return typeof input === "string" ? input.split(",") : input.join(",");
}

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Type System Essentials

Union and Intersection Types

// Union - one of multiple types
type Status = "pending" | "approved" | "rejected";
type Result = string | Error;

// Intersection - combine types
type Timestamped = { createdAt: Date; updatedAt: Date };
type Entity = User & Timestamped;