Inversion_of_control.js

// IoC Container Example
export default class Container {
  constructor() {
    this._services = new Map();
    this._singletons = new Map();
  }
  register(name, definition, dependencies) {
    this._services.set(name, {definition: definition, dependencies: dependencies})
  }

  singleton(name, definition, dependencies) {
    this._services.set(name, {definition: definition, dependencies: dependencies, singleton:true})
  }

  get(name) {
    const c = this._services.get(name);

    if(this._isClass(c.definition)) {

      if(c.singleton) {
        const singletonInstance = this._singletons.get(name);
        if(singletonInstance) {
          return singletonInstance
        } else {
          const newSingletonInstance = this._createInstance(c);
          this._singletons.set(name, newSingletonInstance);
          return newSingletonInstance;
        }
      }

      return this._createInstance(c);

    } else {
      return c.definition;
    }
  }

  _getResolvedDependencies(service) {
    let classDependencies = [];
    if(service.dependencies) {
      classDependencies = service.dependencies.map((dep) => {
        return this.get(dep)
      })
    }
    return classDependencies;
  }

  _createInstance(service) {
    return new service.definition(...this._getResolvedDependencies(service))
  }

  _isClass(definition) {
    return typeof definition === 'function'
  }
}