Defining Typescript types for CommonJS module

Defining TypeScript Types for CommonJS Module

If you are working with TypeScript and using CommonJS modules, you may encounter situations where you need to define types for CommonJS modules. In this blog post, we will explore different solutions to this problem.

Solution 1: Using the `import` statement

One way to define types for CommonJS modules is by using the import statement with the import type syntax. This allows you to import the module and define its type without actually importing any values from the module.

Here’s an example:

import type { MyModuleType } from './my-module';

In this example, we are importing the type MyModuleType from the my-module module. You can then use this type to define variables or function parameters.

Solution 2: Using the `require` function

Another way to define types for CommonJS modules is by using the require function with type assertions. This allows you to require the module and assert its type.

Here’s an example:

const myModule = require('./my-module') as MyModuleType;

In this example, we are requiring the my-module module and asserting its type as MyModuleType. You can then use the myModule variable with the defined type.

Solution 3: Using declaration merging

If you have control over the CommonJS module, you can also define its types using declaration merging. This allows you to extend the existing module type and add your own type definitions.

Here’s an example:

// my-module.d.ts
declare module 'my-module' {
  export interface MyModuleType {
    // your type definitions here
  }
}

In this example, we are creating a declaration file my-module.d.ts and using declaration merging to extend the MyModuleType interface with our own type definitions.

These are three different solutions you can use to define TypeScript types for CommonJS modules. Choose the one that best suits your needs and the structure of your project.

Remember to always keep your TypeScript types up to date with the actual module structure to ensure type safety in your code.

Happy coding!

Defining Typescript types for CommonJS module