Global declarations

Global declarations are used when you want to define types or variables that should be accessible everywhere in your project, without importing them in each file.

🧾 Use Cases

• Declaring global variables, functions, or interfaces.

• Adding custom types to the global Window, NodeJS, or global object.

• Setting types in environments like browsers or Node.js.

📁 How to Set Up

1. Create a file like globals.d.ts or inside types/ folder.

2. Add the following to your tsconfig.json so TypeScript knows about it:

{
  "compilerOptions": {
    "typeRoots": ["./types", "./node_modules/@types"]
  },
  "include": ["src", "types"]  // or wherever your global types are
}

🛠️ Declaring a Global Interface

// types/globals.d.ts
export {};

declare global {
  interface MyGlobalSettings {
    theme: "dark" | "light";
    version: string;
  }

  var appSettings: MyGlobalSettings;
}

Now you can use appSettings anywhere in your code:

console.log(appSettings.theme);

🌐 Example: Global Window Extension

// types/globals.d.ts
export {};

declare global {
  interface Window {
    myAnalytics: () => void;
  }
}

Now window.myAnalytics() will be recognized by TypeScript.

💡 Global Constants and Functions

// types/globals.d.ts
export {};

declare global {
  const __VERSION__: string;
  function logInfo(msg: string): void;
}

Use them globally:

console.log(__VERSION__);
logInfo("App started");

🧩 Node.js Global Declaration

// types/globals.d.ts
export {};

declare global {
  namespace NodeJS {
    interface ProcessEnv {
      NODE_ENV: "development" | "production";
      API_KEY: string;
    }
  }
}

✅ Best Practices

• Wrap your declarations in declare global { ... }.

• Always export {} at the top to make the file a module, which ensures correct scope.

• Don’t pollute the global scope unnecessarily. Use it only for truly global values.