a tiny userland registry, using a "parse" and "link" primitive

a.js

import {b} from "./b.js";
import $ from "jquery";

export function a() {
  // ...
}

b.js

import {a} from "./a.js";
import $ from "jquery";

export function b() {
  // ...
}

tiny-example.js

class TinyLittleRegistry {
  constructor(realm, jquery) {
    this.#realm = realm;
    this.#jquery = jquery;
  }

  @lazy records() {
    return Promise.all([fetch("a.js"), fetch("b.js")])
                  .then(sources => sources.map(s => this.#realm.parseModule(s)));
  }

  @lazy async graph() {
    let { a, b } = await this.records();

    a.link({
      "./b.js": b,
      "jquery": this.#jquery
    });

    b.link({
      "./a.js": a,
      "jquery": this.#jquery
    });
    
    return { a, b };
  }
}

import * as jquery from "jquery";

class TinyLittleRealm extends Realm {
    constructor() {
      super();
      this.#registry = new TinyLittleRegistry(this, jquery);
    }

    [Realm.import](name, referrer) {
      if (["a", "b"].indexOf(name) < 0) {
        throw new ReferenceError("unrecognized module: " + name);
      }
      return this.#registry.graph().then(graph => graph[name]);
    }
}

let realm = new TinyLittleRealm();

realm.eval("import('a')").then(m => m.a());