JS实现三级联动

通过数组简单实现三级联动。代码如下图所示： 

	
		
		
		
	
	
		
			--请选择--
			湖南
			广东
			河南
		
		
			--请选择--
		
		
			--请选择--
		
	

JS代码：

var citys = [
		["长沙","郴州","永州"],
		["广州","惠州","深圳"],
		["郑州","开封","洛阳"]
	];
	var countys = [
		[
			["芙蓉区","雨花区","天心区"],["苏仙区","北湖区","嘉禾县"],["蓝山县","宁远县","道县"]		
		],
		[
			["黄浦区","天河区","番禺区"],["惠城区","惠阳区","博罗县"],["福田区","南山区","宝安区"]
		],
		[
			["中原区","金水区","上街区"],["龙亭区","祥符区","杞县"],["洛龙区","洛宁县","孟津县"]
		]
	];
	function addCitysOpt(text,value){
		//根据id获得city下拉框
		var city = document.getElementById("city");
		//创建下拉选项
		var opt = document.createElement("option");
		//分别赋值
		opt.text = text;
		opt.value = value;
		//将该节点添加到city下拉框节点中
		city.options.add(opt);
	}
	function addCountyOpt(text,value){
		//同上
		var county = document.getElementById("county");
		var opt = document.createElement("option");
		opt.text = text;
		opt.value = value;
		county.options.add(opt);
	}
	function addCity(value){
		//通过id获得省级元素
		var province = document.getElementById("province");
		//通过id获得市级元素
		var city = document.getElementById("city");
		//通过id获得县级元素
		var county = document.getElementById("county");
		//每次联动前，将联动下拉框的长度变为1；
		city.options.length = 1;
		county.options.length = 1;
		//根据value循环citys数组，将对应城市一一添加进城市下拉框。
		for(var i = 0 ; i< citys[value].length; i++){
			addCitysOpt(citys[value][i],i);
		}
	}
	function addCounty(value){
		//同上
		var province = document.getElementById("province");
		var city = document.getElementById("city");
		var county = document.getElementById("county");
		p_value = province.value;
		county.options.length = 1;
		for(var i = 0;i