subpath exports for large packages

[fuxingloh]

What would you like to be added:

Available in NPM >v12.7.0

Custom subpaths can be defined along with the main entry point by treating the main entry point as the "." subpath:

{
  "main": "./dist/index.js",
  "exports": {
    ".": "./dist/index.js",
    "./submodule": "./dist/bech32.js"
  }
}

This allow loading a sub path

import submodule from '@defichain/jellyfish-crypto/bech32';
// Loads ./node_modules/@defichain/jellyfish-crypto/dist/bech32.js

Why is this needed:

As the modules and packages grows, it is becoming increasingly complex to manage imports and exports. Bundling all exports into one index.js file for small modules make senses but for large more complex modules it is harder to effectively manage conflicts. E.g. jellyfish-api-core, hence it is wise to implement subpath exports vs named exports for larger packages.

[fuxingloh]

Subpath exports is not yet supported in typescript, and it seems like it will be part of TypeScript 4.3, May 25 final release.
Let's wait for that.

microsoft/TypeScript#42762