Angular.js DI example

d-fens.js

// Framework

function createInjector() {

  var instanceCache = {};
  var providerCache = {};

  function constant(key, value) {
    instanceCache[key] = value;
  }

  function factory(key, factoryFn) {
    providerCache[key] = factoryFn;
  }

  function service(key, Constructor) {
    factory(key, function() {
      var LocalConstructor = function() { };
      LocalConstructor.prototype = Constructor.prototype;
      var instance = new LocalConstructor();
      invoke(Constructor, instance);
      return instance;
    });
  }

  function invoke(fn, self) {
    var argsString = fn.toString().match(/function\s*[^\(]*\(([^\)]*)\)/)[1];
    var args = argsString.split(',').map(function(arg) {
      return arg.replace(/\s*/g, '');
    });
    var deps = args.map(function(arg) {
      if (instanceCache.hasOwnProperty(arg)) {
        return instanceCache[arg];
      } else if (providerCache.hasOwnProperty(arg)) {
        var provider = providerCache[arg];
        var instance = invoke(provider);
        instanceCache[arg] = instance;
        return instance;
      }
    });
    return fn.apply(self, deps);
  }

  return {
    constant: constant,
    factory: factory,
    service: service,
    invoke: invoke
  };

}

// App


function launchMissiles() {
  console.log('Missiles launched at '+new Date);
};


function BigRedButton(buttonTarget) {
  this.target = buttonTarget;
}
BigRedButton.prototype = {
  openLid: function() { this.open = true; },
  closeLid: function() { this.open = false; },
  press: function() {
    if (this.open) {
      this.target();
    } else {
      throw 'Cannot press while lid closed.'
    }
  }
};


var water = {
  fluoridated: true
};

function defend(substance, button) {
  if (substance.fluoridated) {
    button.openLid();
    button.press();
    button.closeLid();
  }
}


var injector = createInjector();
injector.constant('substance', water);
injector.service('button', BigRedButton);
injector.constant('buttonTarget', launchMissiles);

injector.invoke(defend);