Dependency-injection container example using vanilla JS.

container.js

let uid = 0;

class Foo {
  constructor({ bar }, id) {
    this.uid = uid++;
    this.id = id;
    this.bar = bar;
  }
}

class Bar {
  constructor({ baz }) {
    this.uid = uid++;
    this.baz = baz;
  }
}

const container = {
  // Class instances
  foo(...args) {
    return new Foo(container, ...args);
  },

  // Class singleton
  get bar() {
    return (this._bar ||
      this._bar = new Bar(container)
    );
  },

  // Pojo singleton
  baz: {
    uid: uid++,
    bat: 'qux',
  },
};

console.log('foo', container.foo('a'));
console.log('foo', container.foo('b'));
console.log('bar', container.bar);
console.log('bar', container.bar);
console.log('baz', container.baz);
console.log('baz', container.baz);