Design Pattern
Learn by writing code
Design pattern
// Each of the following options will create a new empty object:
var newObject = {};
// or
var newObject = Object.create( Object.prototype );
// or
var newObject = new Object();Object Creation
// ECMAScript 3 compatible approaches
// 1. Dot syntax
// Set properties
newObject.someKey = "Hello World";
// Get properties
var value = newObject.someKey;
// 2. Square bracket syntax
// Set properties
newObject["someKey"] = "Hello World";
// Get properties
var value = newObject["someKey"];
// ECMAScript 5 only compatible approaches
// For more information see: http://kangax.github.com/es5-compat-table/
// 3. Object.defineProperty
// Set properties
Object.defineProperty( newObject, "someKey", {
value: "for more control of the property's behavior",
writable: true,
enumerable: true,
configurable: true
});
// If the above feels a little difficult to read, a short-hand could
// be written as follows:
var defineProp = function ( obj, key, value ){
var config = {
value: value,
writable: true,
enumerable: true,
configurable: true
};
Object.defineProperty( obj, key, config );
};
// To use, we then create a new empty "person" object
var person = Object.create( Object.prototype );
// Populate the object with properties
defineProp( person, "car", "Delorean" );
defineProp( person, "dateOfBirth", "1981" );
defineProp( person, "hasBeard", false );
console.log(person);
// Outputs: Object {car: "Delorean", dateOfBirth: "1981", hasBeard: false}
// 4. Object.defineProperties
// Set properties
Object.defineProperties( newObject, {
"someKey": {
value: "Hello World",
writable: true
},
"anotherKey": {
value: "Foo bar",
writable: false
}
});
// Getting properties for 3. and 4. can be done using any of the
// options in 1. and 2.// Create a race car driver that inherits from the person object
var driver = Object.create( person );
// Set some properties for the driver
defineProp(driver, "topSpeed", "100mph");
// Get an inherited property (1981)
console.log( driver.dateOfBirth );
// Get the property we set (100mph)
console.log( driver.topSpeed );
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() );Basic Constructor
function Car( model, year, miles ) {
this.model = model;
this.year = year;
this.miles = miles;
}
// Note here that we are using Object.prototype.newMethod rather than
// Object.prototype so as to avoid redefining the prototype object
Car.prototype.toString = function () {
return this.model + " has done " + this.miles + " miles";
};
// Usage:
var civic = new Car( "Honda Civic", 2009, 20000 );
var mondeo = new Car( "Ford Mondeo", 2010, 5000 );
console.log( civic.toString() );
console.log( mondeo.toString() );Constructor with prototype
The Module Pattern
- The Module pattern
- Object literal notation
- AMD modules
- CommonJS modules
- ECMAScript Harmony modules
The Module Pattern
var myObjectLiteral = {
variableKey: variableValue,
functionKey: function () {
// ...
}
};Object Literals
var myModule = {
myProperty: "someValue",
// object literals can contain properties and methods.
// e.g we can define a further object for module configuration:
myConfig: {
useCaching: true,
language: "en"
},
// a very basic method
saySomething: function () {
console.log( "Where in the world is Paul Irish today?" );
},
// output a value based on the current configuration
reportMyConfig: function () {
console.log( "Caching is: " + ( this.myConfig.useCaching ? "enabled" : "disabled") );
},
// override the current configuration
updateMyConfig: function( newConfig ) {
if ( typeof newConfig === "object" ) {
this.myConfig = newConfig;
console.log( this.myConfig.language );
}
}
};
// Outputs: Where in the world is Paul Irish today?
myModule.saySomething();
// Outputs: Caching is: enabled
myModule.reportMyConfig();
// Outputs: fr
myModule.updateMyConfig({
language: "fr",
useCaching: false
});
// Outputs: Caching is: disabled
myModule.reportMyConfig();Module Pattern
var testModule = (function () {
var counter = 0;
return {
incrementCounter: function () {
return counter++;
},
resetCounter: function () {
console.log( "counter value prior to reset: " + counter );
counter = 0;
}
};
})();
// Usage:
// Increment our counter
testModule.incrementCounter();
// Check the counter value and reset
// Outputs: counter value prior to reset: 1
testModule.resetCounter();The Revealing Module Pattern
var myRevealingModule = (function () {
var privateVar = "Ben Cherry",
publicVar = "Hey there!";
function privateFunction() {
console.log( "Name:" + privateVar );
}
function publicSetName( strName ) {
privateVar = strName;
}
function publicGetName() {
privateFunction();
}
// Reveal public pointers to
// private functions and properties
return {
setName: publicSetName,
greeting: publicVar,
getName: publicGetName
};
})();
myRevealingModule.setName( "Paul Kinlan" );The Singleton Pattern
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.The Singleton Pattern
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.JavaScript this object
By Tarun Sharma
