将let first=document.getElementById('first'); let second=document.getElementById('second'); let third=document.getElementById('third'); let xhr=new XMLHttpRequest(); let url='http://10.0.55.125:8081//AjaxDemo/SelectServlet?id='; let loadArea=function(id,areaSelect){ areaSelect.innerHTML="<option value='-1'>---请选择---</option>"; xhr.open('get',url+id,true); xhr.send(null); xhr.onreadystatechange=function(){ if(xhr.readyState==4&&xhr.status==200){ let areas=JSON.parse(xhr.responseText); for(let area of areas){ let newOption=document.createElement('option'); newOption.value=area.id; newOption.innerText=area.name; areaSelect.appendChild(newOption); } } } } first.addEventListener('change',function(e){ loadArea(this.options[this.options.selectedIndex].value,second); },false); second.addEventListener('change',function(e){ loadArea(this.options[this.options.selectedIndex].value,third); },false); loadArea(0,first);转化为jquery ajax

let first=document.getElementById('first');
let second=document.getElementById('second');
let third=document.getElementById('third');
let url='http://10.0.55.125:8081//AjaxDemo/SelectServlet?id=';

let loadArea=function(id, areaSelect){
    areaSelect.html("<option value='-1'>---请选择---</option>");
    $.ajax({
        url: url + id,
        type: 'GET',
        dataType: 'json',
        success: function(areas){
            for(let area of areas){
                let newOption=document.createElement('option');
                newOption.value=area.id;
                newOption.innerText=area.name;
                areaSelect.append(newOption);
            }
        }
    });
};

first.addEventListener('change',function(e){
    loadArea($(this).val(), $(second));
},false);

second.addEventListener('change',function(e){
    loadArea($(this).val(), $(third));
},false);

loadArea(0, $(first));

注意，上述代码需要引入 jQuery 库才能运行。