javascript - 从事件监听器返回一个变量

Question

我有一个 XMLHttpRequests 的通用函数。如下:

function XMLRequest(address, data){
    this.html = "null";
    this.xml = null;
    this.stat = null;
    req = new XMLHttpRequest();

    req.addEventListener('readystatechange', function(this) {

        console.log("from event listener, this.html = "+this.html);
        this.ready = req.readyState;
        if(req.readyState == 4)
        {
            this.stat = req.readyState;
            if(req.status == 200)
            {
                try{
                    this.xml = req.responseXML.documentElement;
                }
                catch(err){
                    this.xml = err;
                }

                try{
                    this.html = req.responseText;
                }catch(err){
                    this.html = err;
                }
                console.log("html = "+this.html);
            }
        }   
    }, false);

    req.open("GET", address+"?"+data, true);
    req.setRequestHeader('content-type', "text/xml");
    req.send();    
    return this;

};

我的想法是使用 watch() 函数来监视 this.html 或 this.xml< 中的更改。然而，我从未看到过变化，并且我意识到了原因；

在匿名监听器函数内部，this 指的是匿名函数，而不是 XMLRequest

我希望找到解决这个问题的方法，以某种方式将 xml 和文本响应从监听器函数中获取到 this.xml 和 this.html XMLRequest 函数，以便我可以监视它

有什么办法可以做到这一点吗？

--编辑--

布拉德的示例，经过我的编辑，供讨论:

function MyObject(){
    this.publicFoo = 'BAR';
    var privateFoo = 'bar';

    var self = this; // store current context so we can reference it in other scopes.
    this.CallMe = function(){
        self.publicFoo = 'newBAR';
        setTimeout(function(){
            alert('public: ' + self.publicFoo + '\nprivate: ' + privateFoo);
        },100);
    };

    return this;
};

var myobj = MyObject();
myobj.CallMe();
alert(myobj.publicFoo)  <-- I want this to alert "newBAR", not "BAR"

Answer 1

在使用之前存储您需要的变量，然后引用它们(就像您通常为避免范围问题所做的那样:

function MyObject(){
    this.publicFoo = 'BAR';
    var privateFoo = 'bar';

    this.CallMe = function(){
        // set them as something referenceable when not within the object's scope
        var iSee_publicFoo = this.publicFoo,
            iSee_privateFoo = privateFoo;

        setTimeout(function(){
            alert('public: ' + iSee_publicFoo + '\nprivate: ' + iSee_privateFoo);
        },100);
    };

    return this;
};

var myobj = MyObject();
myobj.CallMe();

<小时/>

使用var self = this版本:

function MyObject(){
    this.publicFoo = 'BAR';
    var privateFoo = 'bar';

    var self = this; // store current context so we can reference it in other scopes.
    this.CallMe = function(){
        setTimeout(function(){
            alert('public: ' + self.publicFoo + '\nprivate: ' + privateFoo);
        },100);
    };

    return this;
};

var myobj = MyObject();
myobj.CallMe();