TS2304: Cannot find name

Many libraries need @types/package installed for TypeScript to recognize them.

# Install type definitions
npm install --save-dev @types/node
npm install --save-dev @types/express
npm install --save-dev @types/react

# Install everything from DefinitelyTyped for a project
npm install --save-dev @types/

# Check if types are available: https://www.npmjs.com/search?q=%40types

Use declare to tell TypeScript about global variables that exist at runtime.

// For Node.js globals like process, Buffer (install @types/node instead)

// For custom global variables
declare const MY_API_KEY: string

// For window globals
declare global {
  interface Window {
    myAppConfig: { apiUrl: string }
  }
}

// Now you can use them
console.log(window.myAppConfig.apiUrl)

Ensure your tsconfig.json includes the right settings for your project.

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "bundler",
    "types": ["node"],  // Include global types
    "skipLibCheck": true  // Skip checking .d.ts files
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Ensure types are properly exported from their source files and imported where used.

// types.ts
export interface User {
  id: number
  name: string
}

// user.ts
// ❌ Cannot find name User
const user: User = { id: 1, name: "Alice" }

// ✅ Import first
import type { User } from "./types"
const user: User = { id: 1, name: "Alice" }