《JavaScript模式》
/**
* 单体(Singleton)模式的思想在于保证一个特定类仅有一个实例。这意味着当您第二次使用同一个类创建新对象的时候,每次得到与第一次创建对象完全相同对象
* 在JS中没有类,只有对象。当您创建一个新对象时,实际上没有其他对象与其类似,因此新对象已经是单体了
* 在JS中,对象之间永远不会完全相等,除非它们是同一个对象
*/
var obj = {
myprop: 'my value'
}
var obj2 = {
myprop: 'my value'
}
console.log(obj == obj2) // false function Universe() {
if (typeof Universe.instance === 'object') {
return Universe.instance
}
this.start_time = 0
this.bang = 'Big'
Universe.instance = this
// 构造函数隐式返回this
//return this
}
var uni = new Universe()
var uni2 = new Universe()
console.log(uni === uni2) function Universe2() {
var instance = this
this.start_time = 0
this.bang = 'Big'
Universe2 = function() {
return instance
}
}
var uni = new Universe2()
var uni2 = new Universe2()
var uni3 = new Universe2()
var uni4 = new Universe2() // ... 一直执行重写后的构造函数
console.log(uni === uni2) function Universe3() {
var instance
Universe3 = function Universe3() {
return instance
}
Universe3.prototype = this
instance = new Universe3()
instance.constructor = Universe3
instance.start_time = 0
instance.bang = 'Big'
return instance
}
Universe3.prototype.nothing = true
var uni = new Universe3()
Universe3.prototype.everything = true
var uni2 = new Universe3()
console.log('====================\n', uni.nothing, uni.everything, uni.constructor.name, (uni.constructor === Universe3)) var Universe4
;(function() {
var instance
Universe4 = function Universe4() {
if (instance) {
return instance
}
instance = this
this.start_time = 0
this.bang = 'Big'
}
})();
Universe4.prototype.nothing = true
var uni = new Universe4()
Universe4.prototype.everything = true
var uni2 = new Universe4()
console.log('====================\n', uni.nothing, uni.everything, uni.constructor.name, (uni.constructor === Universe4))