js实现简单的级联下拉列表

代码如下：

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script src="js/jquery.min.js" type="text/javascript" charset="utf-8"></script>
		<style type="text/css">
			select{
				width: 150px;
			}
		</style>
	</head>
	<body>
		<select name="firstEn" id="firstEn">
		</select>
		<select name="secondEn" id="secondEn">
			
		</select>
		<script type="text/javascript">
			let data = [
				{
					firstData:'农用动力机械',
					secondData:['内燃机和装备内燃机的拖拉机','电动机','风力机','水轮机和各种小型发电机组']
				},
				{
					firstData:'农用建设机械',
					secondData:['推土机','平地机','铲运机','挖掘机','装载机','凿岩机']
				},
				{
					firstData:'农用耕作机械',
					secondData:['桦式犁','圆盘犁','凿式犁','旋耕机']
				},
				{
					firstData:'农用种植机械',
					secondData:['播种机','栽种机','秧苗栽植机']
				},
				{
					firstData:'农用保护机械',
					secondData:['化学或物理方法除草设备','用物理方法防治病虫害的设备']
				},
				{
					firstData:'农田排灌机械',
					secondData:['水泵','喷灌设备']
				},
				{
					firstData:'谷物联合收获机',
					secondData:['谷物联合收获机','棉花收获机']
				},
				{
					firstData:'农产品加工机械',
					secondData:['碾米机','磨粉机']
				}
			]
			
			//第一个下拉列表的默认
			let oneSelect = 2;
			//给两个下拉列表赋值
			setSelectFn(data,'firstEn',true);
			setSelectFn(data[oneSelect].secondData,'secondEn',false);
			
			//更改第一个下拉列表
			$('#firstEn').change(function(){
				let index = $(this).find('option:selected').attr('key');
				setSelectFn(data[index].secondData,'secondEn',false);
			})
			
			//更改第二个下拉列表
			$('#secondEn').change(function(){
				console.log($('#firstEn option:selected').val())
				console.log($('#secondEn option:selected').val())
			})
			
			
			//设置下拉列表的默认选项
			 $("#firstEn option[key="+oneSelect+"]").prop("selected",true);
			 $("#secondEn option[value='圆盘犁']").prop("selected",true);
			
			
			//填写option选项
			function setSelectFn(array,idName,isFirst){
				let html = '';
				array.forEach((v,k)=>{
					let value;
					if(isFirst){
						value = v.firstData;
					}else{
						value = v;
					}
					html += `<option  key="${k}" value="${value}">${value}</option>`;
					console.log()
				})
				$('#'+idName).html(html);
			}
		</script>
	</body>
</html>

运行结果：