下面的 ajax onreadstatechange() 被调用的情形很诡异，alert 输出
如下：
xhr.open:b.js
readyState=1
readyState=2
readyState=3
readyState=4
status=0
got alert("b.js")
status=0
got alert("b.js")

为什么重复了两次？ firefox 3.5.9。

(function() {
    var i, xhr;

    try {
        xhr = new XMLHttpRequest();     // Firefox, Opera, Safari

        if (xhr.overrideMimeType) {
            // avoid Firefox treating it as text/xml to report a syntax error
            xhr.overrideMimeType('text/javascript; charset=UTF-8');
        }

        alert("<br/>xhr.open: b.js");
        xhr.open('GET', "b.js", true);

        xhr.onreadystatechange = function() {
            alert("<br/>readyState=" + xhr.readyState);

            if (xhr.readyState == 4) {
                xhr.onreadystatechange = function() {};
                i = xhr.status;

                alert("<br/>status=" + i);

                if (i == 200 || i == 0) {
                    script = xhr.responseText;
                    alert("<br/>got " + script);
                }
            }
        }

        xhr.send(null);
    } catch (e) {
        alert(e);
    }

})()
--
FROM 114.249.125.*