php - 如何使用 AJAX 更新选择菜单 w/out inside form

Question

我正在使用 ajax 调用来更新选择菜单。 ajax 调用通过从不同的 .php 文件运行将列表放入我的选择菜单中。

这是 JS 插入片段:

if (req.status == 200) {
        document.getElementById('countydiv').innerHTML=req.responseText;
} else {
        alert("There was a problem while using XMLHTTP:\n" + req.statusText);
}

这是 HTML:

    <label for="county">County:</label>
    <div id="countydiv">
        <select name="county">
            <option>Select State First</option>
        </select>
    </div>

很简单。该脚本有效，但前提是 <div id="countydiv">就在那里。

我怎样才能更改 JavaScript 以继续使用看起来像这样的标记？

    <label for="county">County:</label>
    <select name="county">
    <option>Select State First</option>
    </select>

更新:也许我应该包括整个函数:

function getCounty(stateId) {

    var strURL="findCounty.php?state="+stateId;
    var req = getXMLHTTP();

    if (req) {

            req.onreadystatechange = function() {
                    if (req.readyState == 4) {
                            // only if "OK"
                            if (req.status == 200) {
                                    document.getElementById('countydiv').innerHTML=req.responseText;
                            } else {
                                    alert("There was a problem while using XMLHTTP:\n" + req.statusText);
                            }
                    }
            }
            req.open("GET", strURL, true);
            req.send(null);
    }

和标记:

    <p>
        <label for="state">State:</label>
        <select name="state" onChange="getCounty(this.value)">
                <option>Select State...</option>
                <option>1</option>
                <option>2</option>
                <option>3</option>
        </select>
</p>

<p>
        <label for="county">County:</label>
        <select name="county">
                <option>Select State First</option>
        </select>
</p>

Answer 1

试试这个:

if (req.status == 200) {
        var selects = document.getElementsByTagName("select");
        for(var i=0;i<selects.length;i++) {
            var s = selects[i];
            if(s.name == "county") {
                var replacement = document.createElement("div");
                replacement.innerHTML = req.responseText;
                s.parentNode.insertBefore(s,replacement);
                s.parentNode.removeNode(s);
                break;
            }
        }
        //document.getElementById('countydiv').innerHTML=req.responseText;
} else {
        alert("There was a problem while using XMLHTTP:\n" + req.statusText);
}