Create an Accurate Model of Your Environment

Overview

Your TypeScript environment includes globals, environment variables, and platform-specific APIs. Create accurate type definitions for your environment using declaration files (.d.ts). This ensures type safety for platform-specific code and global variables.

When to Use This Skill

• Defining global types
• Augmenting window or globalThis
• Typing environment variables
• Working with build-time constants
• Configuring type definitions

The Iron Rule

Model your environment accurately with .d.ts files. Declare globals, window properties, and environment variables that your code depends on.

Example

// types/environment.d.ts
declare global {
  interface Window {
    APP_CONFIG: {
      apiUrl: string;
      version: string;
    };
  }
  
  const BUILD_TIMESTAMP: number;
}

// Usage
console.log(window.APP_CONFIG.apiUrl);
console.log(BUILD_TIMESTAMP);

Reference

• Effective TypeScript, 2nd Edition by Dan Vanderkam
• Item 76: Create an Accurate Model of Your Environment