Getting Started

Install & Compile

# Install TypeScript as a dev dependency
npm install typescript --save-dev

# Compile a specific TypeScript file (e.g., app.ts)
npx tsc app.ts

tsc / tsserver

• tsc（TypeScript Compiler）自行把 .ts/.tsx 解析成 TS AST，然后做类型检查、产生 .js 或 .d.ts 等输出。
• tsserver 则在编辑器里作为长驻进程，基于 tsc API 提供 IntelliSense、跳转、重构等语言服务。它用的是同一份 TypeScript Compiler API 的 AST，所以 tsc 和 tsserver“共享”这一套解析/类型引擎。

Configuration

Create a tsconfig.json in your project root. This configuration enables strict type-checking and modern JavaScript features.

{
  "compilerOptions": {
    "target": "ES2020",                          // Use modern JS features
    "module": "ESNext",                          // Use the latest module system
    "moduleResolution": "node",                  // Node module resolution
    "outDir": "./dist",                          // Compiled output directory
    "rootDir": "./",                             // Root of your source files
    "strict": true,                              // Enable all strict type-checking options
    "esModuleInterop": true,                     // Allow default imports from non-ES modules
    "skipLibCheck": true,                        // Skip type checking of declaration files
    "forceConsistentCasingInFileNames": true,    // Enforce consistent file naming
    "resolveJsonModule": true,                   // Import JSON files as modules
    "allowSyntheticDefaultImports": true,        // Allow default imports even if module doesn't have one
    "strictNullChecks": true,                    // Null and undefined are separate types
    "noImplicitAny": true,                       // Disallow variables with an implied any type
    "noUnusedLocals": true,                      // Error on unused locals
    "noUnusedParameters": true,                  // Error on unused function parameters
    "noFallthroughCasesInSwitch": true           // Prevent fall-through in switch cases
  },
  "include": ["src/**/*.ts"],
  "exclude": ["node_modules", "dist"]
} 

Basic Types

Primitive & Extended Types

Primitive Types: boolean, bigint, null, number, string, symbol, undefined

Extended Types: any, unknown, never, void

Example Usage

// Primitive Types
let num: number = 42;
let isDone: boolean = false;
let username: string = "Merrick";

// Array and Tuple
let numbers: number[] = [1, 2, 3];
let tuple: [number, string] = [1, "hello"];

// Object Type
let user: { name: string; age: number } = { name: "Merrick", age: 22 };

// Extended Type - Use sparingly
let anything: any = "This can be any type";

<aside> 💡

Avoid any unless absolutely necessary; prefer unknown when possible.

</aside>

Functions

Declaration & Arrow Functions

Explicit return types make functions easier to read and maintain:

// Function Declaration with explicit return type
function add(a: number, b: number): number {
  return a + b;
}

// Arrow Function with type inference
const multiply = (x: number, y: number): number => x * y;

// Usage examples
console.log(add(5, 3));      // 8
console.log(multiply(5, 3)); // 15