Import Map Loader

.gitignore

node_modules

importmap.json

{
  "imports": {
    "todayis": "node_modules/todayis/index.js"
  },
  "scopes": {
    "node_modules/todayis": {
      "english-days": "node_modules/english-days/index.json"
    }
  }
}

index.js

console.log(require('todayis')((day) => `Hello, today is ${day}!`))

loader.mjs

import module from 'module'
import { createRequire } from 'module';
const require = createRequire(import.meta.url);

const importmap = require('./importmap.json')

const orig = module._resolveFilename
module._resolveFilename = (request, parent, isMain, options) => {
  // Check scopes
  let rent = parent
  while (rent) {
    if (importmap.scopes[rent.path] && importmap.scopes[rent.path][request]) {
      return importmap.scopes[rent.path][request]
    }
    rent = rent.parent
  }

  // Check imports
  if (importmap.imports[request]) {
    return importmap.imports[request]
  }

  // Fall back to filesystem lookup
  return orig.call(module, request, parent, isMain, options)
}

package-lock.json

{
  "name": "hello-today",
  "version": "1.0.0",
  "lockfileVersion": 1,
  "requires": true,
  "dependencies": {
    "english-days": {
      "version": "1.0.0",
      "resolved": "https://registry.npmjs.org/english-days/-/english-days-1.0.0.tgz",
      "integrity": "sha1-0xT5Wfgq8RI9DQntWpDax3q7nhU="
    },
    "todayis": {
      "version": "1.0.0",
      "resolved": "https://registry.npmjs.org/todayis/-/todayis-1.0.0.tgz",
      "integrity": "sha512-rIzf7H5YCvGJMrzCqyjEfwaW8Okn+/xYq5hOTZhtuq2BG13k7IY77g6Qarf5z+xo19SJMFEBm9jaYlZ7VrmdhQ==",
      "requires": {
        "english-days": "^1.0.0"
      }
    }
  }
}

package.json

{
  "name": "hello-today",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "node --experimental-modules --loader ./loader.mjs index.js",
    "debug": "node --inspect --inspect-brk --experimental-modules --loader ./loader.mjs index.js"
  },
  "repository": {
    "type": "git",
    "url": "git+https://gist.github.com/4399b2351c59438db19a8ffb1f3fcdca.git"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "bugs": {
    "url": "https://gist.github.com/4399b2351c59438db19a8ffb1f3fcdca"
  },
  "homepage": "https://gist.github.com/4399b2351c59438db19a8ffb1f3fcdca",
  "dependencies": {
    "todayis": "^1.0.0"
  }
}