javascript-patterns/design-patterns/singleton.html at master · msoftware/javascript-patterns · GitHub

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<!doctype html>

<head>

<title>JavaScript Patterns</title>

</head>

<body>

/* Title: Singleton

Description: restricts object creation for a class to only one instance

var obj = {

myprop:'my value'

};

var obj2 = {

myprop:'my value'

};

obj === obj2; // false

obj == obj2; // false

var uni = new Universe();

var uni2 = new Universe();

uni === uni2; // true

function Universe() {

// do we have an existing instance?

if (typeof Universe.instance === 'object') {

return Universe.instance;

}

// proceed as normal

this.start_time = 0;

this.bang = "Big";

// cache

Universe.instance = this;

// implicit return:

// return this;

}

// testing

var uni = new Universe();

var uni2 = new Universe();

uni === uni2; // true

/*** Instance in a Closure ***/

function Universe() {

// the cached instance

var instance = this;

// proceed as normal

this.start_time = 0;

this.bang = "Big";

// rewrite the contructor

Universe = function () {

return instance;

};

}

function Universe() {

// the cached instance

var instance;

// rewrite the constructor

Universe = function Universe() {

return instance;

};

// carry over the prototype properties

Universe.prototype = this;

// the instance

instance = new Universe();

// reset the constructor pointer

instance.constructor = Universe;

// all the functionality

instance.start_time = 0;

instance.bang = "Big";

return instance;

}

// testing

var uni = new Universe();

var uni2 = new Universe();

uni === uni2; // true

// adding to the prototype

Universe.prototype.nothing = true;

var uni = new Universe();

// again adding to the prototype

// after the initial object is created

Universe.prototype.everything = true;

var uni2 = new Universe();

// only the original prototype was

// linked to the objects

uni.nothing; // true

uni2.nothing; // true

uni.everything; // undefined

uni2.everything; // undefined

// that sounds right:

uni.constructor.name; // "Universe"

// but that's odd:

uni.constructor === Universe; // false

var Universe;

(function () {

var instance;

Universe = function Universe() {

if (instance) {

return instance;

}

instance = this;

// all the functionality

this.start_time = 0;

this.bang = "Big";

};

}());

// reference

// http://www.addyosmani.com/resources/essentialjsdesignpatterns/book/#singletonpatternjavascript

// http://shop.oreilly.com/product/9780596806767.do?sortby=publicationDate

</script>

</body>

</html>

javascript-patterns/design-patterns/singleton.html at master · msoftware/javascript-patterns · GitHub

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