How to fix Cannot augment module 'X' with a non-module declaration in TypeScript

// ❌ Namespace-based (non-module)
declare namespace MyLibrary {
  interface Config {
    // ...
  }
}

// ✓ Module-based (can be augmented)
declare module 'my-library' {
  export interface Config {
    // ...
  }
}

// ❌ Wrong - trying to augment a namespace as a module
declare module 'jquery' {
  interface JQuery {
    customPlugin(): void;
  }
}

// ✓ Correct - augment the namespace directly
declare namespace JQuery {
  interface JQuery {
    customPlugin(): void;
  }
}

// types/augmentation.d.ts

// Add this line to make it a module
export {};

// Now your module augmentation will work
declare module 'some-library' {
  export interface Config {
    newProperty: string;
  }
}

// ❌ Won't work if library exports a value
declare module 'lodash' {
  export interface LoDashStatic {
    customMethod(): void;
  }
}

// ✓ Augment the global interface instead
import lodash from 'lodash';

declare global {
  interface LoDashStatic {
    customMethod(): void;
  }
}

export {};

# Check installed versions
npm list library-name @types/library-name

# Update @types to match library version
npm install -D @types/library-name@latest

# Or match specific version
npm install -D @types/[email protected]

// types/library-name.d.ts
declare module 'library-name' {
  export interface Config {
    // Copy original properties
    existingProp: string;
    // Add your new properties
    customProp: number;
  }

  export function initialize(config: Config): void;
}