23. What are module declarations, and how can you use them to include non-TypeScript files?

Module declarations in TypeScript allow integration with files that are not written in TypeScript, such as JavaScript, CSS, or JSON files. By using module declarations, we can define types for these files so that TypeScript can recognize them.

Example of a module declaration for a JSON file:

declare module '*.json' {
  const value: any;
  export default value;
}

In this case, we declare that files with a .json extension will be treated as modules with a value of type any. This allows TypeScript to understand JSON files and avoid errors when importing them.

Module declarations are useful when working with external files that are not written in TypeScript but still want to maintain type safety.