单例模式

Sun, Dec 8, 2019

实现单例模式

// 方式1
var Singleton = function(name) {
    this.name = name;
    this.instance = null;
};
Singleton.prototype.getName = function() {
    alert(this.name)
}
Singleton.getInstance = function(name) {
    if(!this.instance) {
        this.instance = new Singleton(name)
    }
    return this.instance;
}

var a = Singleton.getInstance("a");
var b = Singleton.getInstance("b");
a === b // true

// 方式2
var Singleton = function(name) {
    this.name = name;
};
Singleton.prototype.getName = function() {
    alert(this.name)
}
Singleton.getInstance = (function(name) {
    var instance = null;
    return function(name) {
        if(!this.instance) {
            this.instance = new Singleton(name)
        }
    }
    return this.instance;
})();
var a = Singleton.getInstance("a");
var b = Singleton.getInstance("b");
a === b // true

// 缺点：使用者需要知道使用getInstance方法创建单例类

透明的单例模式

var Singleton = (function(){
    var instance = null;
    var Singleton = function() {
        if(instance) {
            return instance;
        }
        return instance = this;
    }
    // 原型链方法
    Singleton.prototype
    return Singleton;
})();

var a = Singleton.getInstance("a");
var b = Singleton.getInstance("b");
a === b // true

// 缺点: 程序复杂

js中的单例模式

// 单例即对象，使用对象就是单例了
var a = {
    get: function() {

    }
}

惰性单例

var getSingle =  (function(fn) {
    var result;
    return function(fn){
        return result || (result = fn.apply(this,arguments))
    }
})();

// 创建iframe

getSingle(function() {
    var iframe = document.createElement("iframe");
    document.body.appendChild(iframe);
    return iframe
})