package.json

{
  main: "cjs",
  module: "esm node",
  browser: "esm browser",
  unpkg: "umd",
  "exports": {
    ".": {
      "browser": {
        "import": "esm browser",
        "require": "cjs browser"
      },
      "import": "esm node",
      "require": "cjs node"
     },
    },
    "./foobar": { ... },
    "./package.json": "./package.json"
  }
}