How to fix Module augmentation requires 'declare module' syntax in TypeScript

Change from regular module syntax to declare module syntax:

// Wrong:
module "some-module" {
  export interface ExtendedInterface {
    newProperty: string;
  }
}

// Correct:
declare module "some-module" {
  export interface ExtendedInterface {
    newProperty: string;
  }
}

Module augmentations typically belong in .d.ts files or files with declare global. If you're augmenting in a regular .ts file, move the augmentation to a declaration file:

// Create a file: src/types/some-module.d.ts
declare module "some-module" {
  // Your augmentations here
}

Or use declare global for global augmentations:

declare global {
  namespace SomeNamespace {
    // Your augmentations here
  }
}

The module path in your declaration must match how the module is imported. Check for exact string matching:

// If you import like this:
import * as lib from "some-library";

// Your augmentation should be:
declare module "some-library" {
  // ...
}

// Not:
declare module "some-library/dist/index" {
  // ...
}

Use the exact same module specifier that appears in your import statements.

Some modules may not support augmentation if they don't have existing declarations or use specific module systems. Verify the module has existing declarations you can extend:

1. Check if the module has type definitions (look for @types/ package or .d.ts files)
2. Ensure you're not trying to augment a module that uses export = syntax (CommonJS default exports)
3. For global augmentations, ensure you're not conflicting with existing declarations

Different declaration types require different merging approaches:

// Adding to an existing interface:
declare module "some-module" {
  interface ExistingInterface {
    newMethod(): void;
  }
}

// Adding new exports:
declare module "some-module" {
  export function newFunction(): string;
}

// Adding to a namespace:
declare module "some-module" {
  namespace SubNamespace {
    interface NewInterface {
      property: boolean;
    }
  }
}

Make sure your augmentation syntax matches the existing module structure.

After fixing the syntax, test that your augmentation works:

1. Create a test file that imports the augmented module
2. Verify TypeScript recognizes your new declarations
3. Check that auto-completion works for the augmented members
4. Ensure no type errors appear when using the augmented functionality

Example test:

import * as lib from "some-module";

// This should now work without type errors
const result = lib.newFunction();
const obj: lib.ExtendedInterface = {
  existingProperty: "value",
  newProperty: "new value" // This property comes from your augmentation
};