design patterns

design-patterns-js

// Constructor

function Car( model, year, miles ) {
 
  this.model = model;
  this.year = year;
  this.miles = miles;
 
  this.toString = function () {
    return this.model + " has done " + this.miles + " miles";
  };
}
 
// Usage:
 
// We can create new instances of the car
var civic = new Car( "Honda Civic", 2009, 20000 );
var mondeo = new Car( "Ford Mondeo", 2010, 5000 );
 
// and then open our browser console to view the
// output of the toString() method being called on
// these objects
console.log( civic.toString() );
console.log( mondeo.toString() );

module-private-var

var basketModule = (function () {
 
  // privates
 
  var basket = [];
 
  function doSomethingPrivate() {
    //...
  }
 
  function doSomethingElsePrivate() {
    //...
  }
 
  // Return an object exposed to the public
  return {
 
    // Add items to our basket
    addItem: function( values ) {
      basket.push(values);
    },
 
    // Get the count of items in the basket
    getItemCount: function () {
      return basket.length;
    },
 
    // Public alias to a private function
    doSomething: doSomethingPrivate,
 
    // Get the total value of items in the basket
    getTotal: function () {
 
      var q = this.getItemCount(),
          p = 0;
 
      while (q--) {
        p += basket[q].price;
      }
 
      return p;
    }
  };
})();

// basketModule returns an object with a public API we can use
 
basketModule.addItem({
  item: "bread",
  price: 0.5
});
 
basketModule.addItem({
  item: "butter",
  price: 0.3
});
 
// Outputs: 2
console.log( basketModule.getItemCount() );
 
// Outputs: 0.8
console.log( basketModule.getTotal() );
 
// However, the following will not work:
 
// Outputs: undefined
// This is because the basket itself is not exposed as a part of our
// public API
console.log( basketModule.basket );
 
// This also won't work as it only exists within the scope of our
// basketModule closure, but not in the returned public object
console.log( basket );

observer

function ObserverList(){
  this.observerList = [];
}
 
ObserverList.prototype.add = function( obj ){
  return this.observerList.push( obj );
};
 
ObserverList.prototype.count = function(){
  return this.observerList.length;
};
 
ObserverList.prototype.get = function( index ){
  if( index > -1 && index < this.observerList.length ){
    return this.observerList[ index ];
  }
};
 
ObserverList.prototype.indexOf = function( obj, startIndex ){
  var i = startIndex;
 
  while( i < this.observerList.length ){
    if( this.observerList[i] === obj ){
      return i;
    }
    i++;
  }
 
  return -1;
};
 
ObserverList.prototype.removeAt = function( index ){
  this.observerList.splice( index, 1 );
};

function Subject(){
  this.observers = new ObserverList();
}
 
Subject.prototype.addObserver = function( observer ){
  this.observers.add( observer );
};
 
Subject.prototype.removeObserver = function( observer ){
  this.observers.removeAt( this.observers.indexOf( observer, 0 ) );
};
 
Subject.prototype.notify = function( context ){
  var observerCount = this.observers.count();
  for(var i=0; i < observerCount; i++){
    this.observers.get(i).update( context );
  }
};

prototype

var vehiclePrototype = {
 
  init: function ( carModel ) {
    this.model = carModel;
  },
 
  getModel: function () {
    console.log( "The model of this vehicle is.." + this.model);
  }
};
 
 
function vehicle( model ) {
 
  function F() {};
  F.prototype = vehiclePrototype;
 
  var f = new F();
 
  f.init( model );
  return f;
 
}
 
var car = vehicle( "Ford Escort" );
car.getModel();

pubsub

var pubsub = {};
 
(function(myObject) {
 
    // Storage for topics that can be broadcast
    // or listened to
    var topics = {};
 
    // A topic identifier
    var subUid = -1;
 
    // Publish or broadcast events of interest
    // with a specific topic name and arguments
    // such as the data to pass along
    myObject.publish = function( topic, args ) {
 
        if ( !topics[topic] ) {
            return false;
        }
 
        var subscribers = topics[topic],
            len = subscribers ? subscribers.length : 0;
 
        while (len--) {
            subscribers[len].func( topic, args );
        }
 
        return this;
    };
 
    // Subscribe to events of interest
    // with a specific topic name and a
    // callback function, to be executed
    // when the topic/event is observed
    myObject.subscribe = function( topic, func ) {
 
        if (!topics[topic]) {
            topics[topic] = [];
        }
 
        var token = ( ++subUid ).toString();
        topics[topic].push({
            token: token,
            func: func
        });
        return token;
    };
 
    // Unsubscribe from a specific
    // topic, based on a tokenized reference
    // to the subscription
    myObject.unsubscribe = function( token ) {
        for ( var m in topics ) {
            if ( topics[m] ) {
                for ( var i = 0, j = topics[m].length; i < j; i++ ) {
                    if ( topics[m][i].token === token ) {
                        topics[m].splice( i, 1 );
                        return token;
                    }
                }
            }
        }
        return this;
    };
}( pubsub ));

// Another simple message handler
 
// A simple message logger that logs any topics and data received through our
// subscriber
var messageLogger = function ( topics, data ) {
    console.log( "Logging: " + topics + ": " + data );
};
 
// Subscribers listen for topics they have subscribed to and
// invoke a callback function (e.g messageLogger) once a new
// notification is broadcast on that topic
var subscription = pubsub.subscribe( "inbox/newMessage", messageLogger );
 
// Publishers are in charge of publishing topics or notifications of
// interest to the application. e.g:
 
pubsub.publish( "inbox/newMessage", "hello world!" );
 
// or
pubsub.publish( "inbox/newMessage", ["test", "a", "b", "c"] );
 
// or
pubsub.publish( "inbox/newMessage", {
  sender: "hello@google.com",
  body: "Hey again!"
});
 
// We can also unsubscribe if we no longer wish for our subscribers
// to be notified
pubsub.unsubscribe( subscription );
 
// Once unsubscribed, this for example won't result in our
// messageLogger being executed as the subscriber is
// no longer listening
pubsub.publish( "inbox/newMessage", "Hello! are you still there?" );

singleton

var mySingleton = (function () {
 
  // Instance stores a reference to the Singleton
  var instance;
 
  function init() {
 
    // Singleton
 
    // Private methods and variables
    function privateMethod(){
        console.log( "I am private" );
    }
 
    var privateVariable = "Im also private";
 
    var privateRandomNumber = Math.random();
 
    return {
 
      // Public methods and variables
      publicMethod: function () {
        console.log( "The public can see me!" );
      },
 
      publicProperty: "I am also public",
 
      getRandomNumber: function() {
        return privateRandomNumber;
      }
 
    };
 
  };
 
  return {
 
    // Get the Singleton instance if one exists
    // or create one if it doesn't
    getInstance: function () {
 
      if ( !instance ) {
        instance = init();
      }
 
      return instance;
    }
 
  };
 
})();
 
var myBadSingleton = (function () {
 
  // Instance stores a reference to the Singleton
  var instance;
 
  function init() {
 
    // Singleton
 
    var privateRandomNumber = Math.random();
 
    return {
 
      getRandomNumber: function() {
        return privateRandomNumber;
      }
 
    };
 
  };
 
  return {
 
    // Always create a new Singleton instance
    getInstance: function () {
 
      instance = init();
 
      return instance;
    }
 
  };
 
})();
 
 
// Usage:
 
var singleA = mySingleton.getInstance();
var singleB = mySingleton.getInstance();
console.log( singleA.getRandomNumber() === singleB.getRandomNumber() ); // true
 
var badSingleA = myBadSingleton.getInstance();
var badSingleB = myBadSingleton.getInstance();
console.log( badSingleA.getRandomNumber() !== badSingleB.getRandomNumber() ); // true
 
// Note: as we are working with random numbers, there is a
// mathematical possibility both numbers will be the same,
// however unlikely. The above example should otherwise still
// be valid.

sub classing

var Person = function( firstName, lastName ){
 
  this.firstName = firstName;
  this.lastName = lastName;
  this.gender = "male";
 
};

// a new instance of Person can then easily be created as follows:
var clark = new Person( "Clark", "Kent" );
 
// Define a subclass constructor for for "Superhero":
var Superhero = function( firstName, lastName, powers ){
 
    // Invoke the superclass constructor on the new object
    // then use .call() to invoke the constructor as a method of
    // the object to be initialized.
 
    Person.call( this, firstName, lastName );
 
    // Finally, store their powers, a new array of traits not found in a normal "Person"
    this.powers = powers;
};
 
Superhero.prototype = Object.create( Person.prototype );
var superman = new Superhero( "Clark", "Kent", ["flight","heat-vision"] );
console.log( superman );
 
// Outputs Person attributes as well as powers