为什么这个 ajax 调用不能在这个简单的 object 文字 ajax 框架中为 ZDE9B9ED78D7E2E1DCEEFFEE71 工作

Question

var ajax = {
xmlHTTP: function() {
    xml = new XMLHttpRequest();
    return xml;
},
xmlHTTPfunction: function() {
    if (xml.readyState == 4 && xml.status == 200)  {
        document.getElementById("te").innerHTML = xml.responseText; 
         alert(xml.status);
         alert(xml.responseText);
     }

},
xmlHTTPopen: function(url) {
    xml.open("POST", url, true);
},
xmlHTTPheader: function() {
    ajax.xmlHTTP().setRequestHeader("Content-type","application/x-www-form-urlencoded");
},
xmlHTTPsend: function(string) {
    xml.send(string);
},
ajaxCall: function() {
    ajax.xmlHTTP();
    ajax.xmlHTTPopen('testx.php');
    ajax.xmlHTTPsend('test');
    return 1;
}
}
   if(ajax.ajaxCall() == 1) {
document.getElementById("te").innerHTML = xml.responseText; 

}

Answer 1

Most of the functions refer to the xml variable which is poorly scoped. That is to say, when you call ajax.xmlHTTPopen there's nothing to say that the xml variable has any value inside said function.

The simplest way to provide better scoping would be to define the xml variable as a property of the ajax object; here is an example with minimal changes to your code:

var ajax = {
    xmlHTTP: function() {
        this.xml = new XMLHttpRequest();
        this.xml.onreadystatechange = this.xmlHTTPfunction();
    },
    xmlHTTPfunction: function() {
        if (this.xml.readyState == 4 && this.xml.status == 200)  {
            document.getElementById("te").innerHTML = this.xml.responseText; 
             alert(this.xml.status);
             alert(this.xml.responseText);
         }
    },
    xmlHTTPopen: function(url) {
        this.xml.open("POST", url, true);
    },
    xmlHTTPheader: function() {
        this.xml.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    },
    xmlHTTPsend: function(string) {
        this.xml.send(string);
    },
    ajaxCall: function() {
        ajax.xmlHTTP();
        ajax.xmlHTTPopen('testx.php');
        ajax.xmlHTTPsend('test');
        return 1;
    }
}

Note that, as you've written it, the ajax.ajaxCall is non-blocking, so it will always return 1 immediately, even before the response arrives (or is necessarily sent) -- to that end, you have to assign a callback function to the XMLHtpRequest object's onreadystatechange event, to handle the response when it eventually comes back.

If you change the third parameter of xml.open to false the xml.send call will block until a response arrives, in which case you don't need to assign a callback. The alternative implementation may look like this:

var ajax = {
    xmlHTTP: function() {
        this.xml = new XMLHttpRequest();
    },
    xmlHTTPopen: function(url) {
        this.xml.open("POST", url, false);
    },
    xmlHTTPheader: function() {
        this.xml.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    },
    xmlHTTPsend: function(string) {
        this.xml.send(string);
    },
    ajaxCall: function() {
        ajax.xmlHTTP();
        ajax.xmlHTTPopen('testx.php');
        ajax.xmlHTTPsend('test');
        return 1;
    }
}
if(ajax.ajaxCall() == 1) {
    document.getElementById("te").innerHTML = ajax.xml.responseText; 
}

However in my experience, this is almost never used in the real world.

Also : your code never calls the xmlHTTPheader function, although there's no harm in that.

I can't think of a better proposal given your current code; have you looked at jQuery and its implementation of ajax?

Answer 2

Some issues:

1. You should really not be relying on a global variable ("xml") to tie everything together. What happens when you want 2 overlapping requests?
2. You're never setting up the "readyStateChange" handler.