javascript - JavaScript 中的动态实例化

Question

我查看了其他在线示例，但它们不起作用。

所以...

我正在尝试在 JavaScript 中实现“Head First”中的经典“装饰器模式”...而且我真的很接近。

鉴于以下“类别”:

// "CLASSES": BEVERAGES
function DarkRoast(){
    this.cost = 1.00;
    this.description = "Dark Roast";
};

// DECORATORS: CONDIMENTS
function Milk(beverage){
    var instance = beverage;
    beverage.cost = function(){
        return instance.cost + 0.25;
    };
    beverage.description = functionn(){
        return instance.description + ', Milk';
    };
};

问题:如何从以下函数动态实例化“Milk”？

function appendCondiment(className, beverage) {
    /* Needs to do this, but dynamically:
        var instance = new Milk(beverage); */

    // This fails (of course)
    var instance = new window[className].call(beverage);
}

Answer 1

您需要:

var instance = new window[className](beverage);