ESM version

[MatthiasKunnen]

Currently, ms is written in CommonJS. This has some drawbacks:

• They cannot be treeshaken properly resulting in larger bundles ^[1]
• It requires esModuleInterop for TypeScript ^[2]
• They are not in the ECMAScript spec as opposed to ESModules ^[3][4] for which support is being built into browsers^[4] and Node^[5]

What I propose is to use the main and module field in package.json to provide both ESM and CommonJS. This change is fully backwards compatible and can be achieved by using TypeScript, Webpack, or Rollup. I'd propose to go the TypeScript way which has the added benefit of type safety and allows ms to bundle types.

If you would accept this I could make a PR.

[theoludwig]

Great suggestion!:+1:

I would suggest that we rewrite the package in TypeScript, so we can include types declarations builtin and deprecate @types/ms.