javascript - 为 JavaScript 对象编写枚举器

Question

我正在尝试了解如何编写 JavaScript 对象的枚举器。我偶然发现了一段 Sharepoint code where items of a SP List were being obtained on the client side ，并且在 Sharepoint 对象上执行了类似于下面的代码。

var enumerator = list.getEnumerator();
while(enumerator.moveNext()) {
    var currentItem = enumerator.getCurrent();
    // actions on currentItem
}

如果我可以编写一个自定义对象，可以像上面那样使用枚举器进行迭代，它会是什么样子？这是我的尝试，但它不起作用:

var list = {
    items: ["A", "B", "C", "D", "E"],
    counter: -1,
    enumerator: {
        moveNext: function() {
            counter++; // outer object's variable not accessible
            if(counter >= items.length)
                return false;
            else
                return true;
        },
        getCurrent: function() {
            return items[counter]; // outer object's variable not accessible
        }
    },
    getEnumerator: function() { 
        return this.enumerator(); 
    }
}

var enumerator = list.getEnumerator();
while(enumerator.moveNext()) {
    var currentItem = enumerator.getCurrent();
    alert(currentItem);
}

你能帮我理解如何将 getEnumerator() 写成适用于任何可枚举对象的函数原型(prototype)吗？

Answer 1

尝试以下:

var list = function() {
    // these local variables could be accessed by inner functions.
    var items = ["A", "B", "C", "D", "E"],
        counter =  -1;
    return {
        enumerator: {
            moveNext: function() {
                counter++; 
                return counter < items.length;
            },
            getCurrent: function() {
                return items[counter]; 
            }
        },
        getEnumerator: function() { 
            // here should not be return this.enumerator() but just this.enumerator
            return this.enumerator; 
        }
    };
};

var enumerator = list().getEnumerator();
while(enumerator.moveNext()) {
    var currentItem = enumerator.getCurrent();
    alert(currentItem);
}

THE JSFIDDLE DEMO.