细节：js 函数闭包内存泄露的解决办法举例

原始代码：

function Cars(){
    this.name = "Benz";
    this.color = ["white","black"];
}
Cars.prototype.sayColor = function(){
    var outer = this;
    return function(){
        return outer.color
    };
};

var instance = new Cars();
console.log(instance.sayColor()())

优化后的代码：

function Cars(){
    this.name = "Benz";
    this.color = ["white","black"];
}
Cars.prototype.sayColor = function(){
    var outerColor = this.color; //保存一个副本到变量中
    return function(){
        return outerColor; //应用这个副本
    };
    outColor = null; //释放内存
};

var instance = new Cars();
console.log(instance.sayColor()())

---

稍微复杂一点的例子：

function inheritPrototype(subType,superType){
    var prototype = Object(superType.prototype);
    prototype.constructor = subType;
    subType.prototype = prototype;
}

function Cars(){
    this.name = "Benz";
    this.color = ["white","black"];
}
Cars.prototype.sayColor = function(){
    var outer = this;
    return function(){
        return outer.color;
    };
};

function Car(){
    Cars.call(this);
    this.number = [321,32];
}
inheritPrototype(Car,Cars);
Car.prototype.sayNumber = function(){
    var outer = this;
    return function(){
        return function(){
            return outer.number[outer.number.length - 1];
        }
    };
};

var instance = new Car();
console.log(instance.sayNumber()()());

首先，该例子组合使用了构造函数模式和原型模式创建Cars 对象，并用了寄生组合式继承模式来创建Car 对象并从Cars 对象获得属性和方法的继承；

其次，建立一个名为instance 的Car 对象的实例；instance 实例包含了sayColor 和sayNumber 两种方法；

最后，两种方法中，前者使用了一个闭包，后者使用了两个闭包，并对其this 进行修改使其能够访问到this.color 和this.number。

这里存在内存泄露问题，油画后的代码如下：

function inheritPrototype(subType,superType){
    var prototype = Object(superType.prototype);
    prototype.constructor = subType;
    subType.prototype = prototype;
}

function Cars(){
    this.name = "Benz";
    this.color = ["white","black"];
}
Cars.prototype.sayColor = function(){
    var outerColor = this.color; //这里
    return function(){
        return outerColor; //这里
    };
    this = null; //这里
};

function Car(){
    Cars.call(this);
    this.number = [321,32];
}
inheritPrototype(Car,Cars);
Car.prototype.sayNumber = function(){
    var outerNumber = this.number; //这里
    return function(){
        return function(){
            return outerNumber[outerNumber.length - 1]; //这里
        }
    };
    this = null; //这里
};

var instance = new Car();
console.log(instance.sayNumber()()());