Question

我无法弄清楚为什么request.onreadystate函数内部的所有内容都可以运行，但是以下的alert（）却没有。该脚本似乎在if语句之后中断。

我真的很感谢有人为我查看我的代码。非常感谢。

    function positionHandler(position) {
        if (!document.getElementById("span")) document.body.appendChild(document.createElement("span"));            
        document.getElementsByTagName("span")[0].innerHTML = "("+position.coords.latitude+","+position.coords.longitude+")";
        request = new XMLHttpRequest();
        request.asycnc = false;
        request.open('GET','get.php?latitude='+position.coords.latitude+'&longitude='+position.coords.longitude);
        request.onreadystatechange = function() {
            if (request.readyState != 4) return false;
            else if (request.readyState == 4 && request.status == 200) {
                var results = request.responseXML.getElementsByTagName('note');
                for (var i in results) {
                    if (!document.getElementById(results[i].getAttribute('id'))) {
                        var note = document.createElement('div');
                        note.innerHTML = results[i].childNodes[2].childNodes[0].nodeValue;
                        note.id = results[i].getAttribute('id');
                        document.getElementById('main').appendChild(note);
                        //everything up until this point works
                    }
                }
                alert("this doesn't work 1");
            }
            alert("this doesn't work 2");
        }
        request.send(null);
        alert("this does work!");
    }

    var position = navigator.geolocation.watchPosition(positionHandler);

Answer 1

尝试更改语句的顺序。

function positionHandler(position) {
    if (!document.getElementById("span")) document.body.appendChild(document.createElement("span"));            
    document.getElementsByTagName("span")[0].innerHTML = "("+position.coords.latitude+","+position.coords.longitude+")";
    request = new XMLHttpRequest();
    request.asycnc = false;
    // set the eventhandler logic
    request.onreadystatechange = function() {
        if (request.readyState != 4) return false;
        else if (request.readyState == 4 && request.status == 200) {
            var results = request.responseXML.getElementsByTagName('note');
            for (var i in results) {
                if (!document.getElementById(results[i].getAttribute('id'))) {
                    var note = document.createElement('div');
                    note.innerHTML = results[i].childNodes[2].childNodes[0].nodeValue;
                    note.id = results[i].getAttribute('id');
                    document.getElementById('main').appendChild(note);
                    //everything up until this point works
                }
            }
            alert("this doesn't work 1");
        }
        alert("this doesn't work 2");
    }
    // the event will be triggered here
    request.open('GET','get.php?latitude='+position.coords.latitude+'&longitude='+position.coords.longitude);
    request.send(null);
    alert("this does work!");
}

var position = navigator.geolocation.watchPosition(positionHandler);

原因是你在request.open(...)语句调用后设置处理程序。

希望这有帮助。

Answer 2

这一行 - ＆gt;警报（“这不起作用1”）;不会起作用，因为循环可能是无限的。这一行 - ＆gt;警报（“这不起作用2”）;仅在此条件else if (request.readyState == 4 && request.status == 200)为假时才有效。

如果您修复了第一个警报问题，第三个警报应该有效。请检查你的循环。

最佳，

在if语句之后破解Javascript

2 个答案: