Node.js architecture blog post (container.js)

container.js

import R from 'ramda';

export default class Container {
  constructor() {
    this.contents = {};
  }

  get(name) {
    if (!(name in this.contents)) {
      throw Error('Container has nothing registered for key ' + name);
    }
    return this.contents[name];
  }

  set(name, instance) {
    this.contents[name] = instance;
  }

  create(klass) {
    if (!('length' in klass.dependencies)) {
      throw new Error('Invariant: container can\'t resolve a class without dependencies');
    }

    var dependencies = R.map(function(dependencyName) {
      return this.get(dependencyName);
    }.bind(this), klass.dependencies);

    return applyToConstructor(klass, dependencies)
  }

  load(klass) {
    if (typeof klass.dependencyName !== 'string') {
      throw new Error('Invariant: container can\'t resolve a class without a name');
    }

    this.set(klass.dependencyName, this.create(klass));
  }

  unset(name) {
    delete this.contents[name]
  }

  reset() {
    this.contents = {};
  }
}

function applyToConstructor(constructor, args) {
  var newObj = Object.create(constructor.prototype);
  var constructorReturn = constructor.apply(newObj, args);

  // Some constructors return a value; let's make sure we use it!
  return constructorReturn !== undefined ? constructorReturn : newObj;
}