Ajax实现简单下拉选项

<script>
	var xhr = getXhr();
	// 第一次执行Ajax异步请求 - 省份
	window.onload = function(){
		xhr.open("get","finaly.php?state=1");
		xhr.send(null);
		xhr.onreadystatechange = function(){
		if(xhr.readyState==4&&xhr.status==200){
				var data = xhr.responseText;
				// 将字符串转换为数组
				var provinces = data.split(",");
				// 遍历数组
				for(var i=0;i<provinces.length;i++){
					// 创建option元素添加到id为province元素上
					var option = document.createElement("option");
					var text = document.createTextNode(provinces[i]);
					option.appendChild(text);
					var province = document.getElementById("province");
					province.appendChild(option);
				}
			}	
		}
	}
	// 第二次执行Ajax异步请求 - 城市
	var provinceEle=document.getElementById("province");
	provinceEle.onchange = function(){
		var city = document.getElementById("city");
		var opts = city.getElementsByTagName("option");
		for(var z=opts.length-1;z>0;z--){
			city.removeChild(opts[z]);
		}
		
		if(province.value != "请选择"){
			xhr.open("post","finaly.php");
			xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
			xhr.send("province="+province.value);
			xhr.onreadystatechange = function(){
				if(xhr.readyState==4&&xhr.status==200){
					var data = xhr.responseText;
					var cities = data.split(",");
					for(var i=0;i<cities.length;i++){
						var option = document.createElement("option");
						var text = document.createTextNode(cities[i]);
						option.appendChild(text);
						
						city.appendChild(option);
					}
				}
			}
		}

	}

	function getXhr(){
		var xhr = null;
		if(window.XMLHttpRequest){
			xhr = new XMLHttpRequest();
		}else{
			xhr = new ActiveXObject("Microsoft.XMLHttp");
		}
		return xhr;
	}
  </script>

<?php
	// 接收客户端发送的请求数据 - state
	$state = $_REQUEST[‘state‘];
	// 判断$state的值
	if($state == 1){// 获取省份
		echo ‘山东省,辽宁省,吉林省‘;
	}else{// 获取城市
		$province = $_POST[‘province‘];
		switch ($province){
			case ‘山东省‘:
				echo ‘青岛市,济南市,威海市,日照市,德州市‘;
				break;
			case ‘辽宁省‘:
				echo ‘沈阳市,大连市,铁岭市,丹东市,锦州市‘;
				break;
			case ‘吉林省‘:
				echo ‘长春市,松原市,吉林市,通化市,四平市‘;
				break;
		}
	}
?>