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How to use JavaScript to create a dynamic drop-down menu effect

一个新手Original: 2017-09-26 10:10:463185browse

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8">
    <title>利用二维数组创建动态下拉菜单</title>
    <script type="text/javascript">
        //定义一个二维数组aCity,用于存储城市名称        
        var aCity=new Array();        
        aCity[0]=new Array();        
        aCity[1]=new Array();        
        aCity[2]=new Array();        
        aCity[3]=new Array();        
        aCity[4]=new Array();        
        aCity[5]=new Array();        //赋值,每个省份的城市存放在用于数组的一行        
        aCity[0][0]="--请选择--";        
        aCity[1][0]="--请选择--";        
        aCity[1][1]="东城区";       
        aCity[1][2]="西城区";        
        aCity[1][3]="朝阳区";        
        aCity[1][4]="海淀区";        
        aCity[1][5]="丰台区";        
        aCity[2][0]="--请选择--";        
        aCity[2][1]="福田区";        
        aCity[2][2]="罗湖区";        
        aCity[2][3]="南山区";        
        aCity[2][4]="宝安区";        
        aCity[2][5]="龙岗区";        
        aCity[2][6]="盐田区";        
        aCity[3][0]="--请选择--";       
         aCity[3][1]="越秀区";        
         aCity[3][2]="东山区";        
         aCity[3][3]="海珠区";        
         aCity[3][4]="荔湾区";        
         aCity[3][5]="天河区";        
         aCity[3][6]="白云区";        
         aCity[4][0]="--请选择--";        
         aCity[4][1]="西湖区";        
         aCity[4][2]="上城区";       
          aCity[4][3]="下城区";        
          aCity[4][4]="江干区";        
          aCity[4][5]="拱墅区";        
          aCity[4][6]="滨江区";        
          aCity[5][0]="--请选择--";        
          aCity[5][1]="新城区";        
          aCity[5][2]="碑林区";        
          aCity[5][3]="莲湖区";        
          aCity[5][4]="雁塔区";        
          aCity[5][5]="灞桥区";        
          aCity[5][6]="长安区";        
          aCity[5][7]="周至县";        
          function ChangeCity(){            
          var i,iProvinceIndex;            
          iProvinceIndex=document.frm.optProvince.selectedIndex;            
          iCityCount=0;            
          while(aCity[iProvinceIndex][iCityCount]!=null)                
          iCityCount++;                //计算选定省份的城市个数                
          document.frm.optCity.length=iCityCount; //改变下拉菜单的选项数                
          for(i = 0;i<=iCityCount-1;i++)  //改变下拉菜单的内容                    
          document.frm.optCity[i]=new Option(aCity[iProvinceIndex][i]);                    
          document.frm.optCity.focus();
        }    </script></head><body onfocus="ChangeCity()">
    <h3>选择省份及城市</h3>
    <form name="frm">
        <p>省份:        <select name="optProvince" size="1" onchange="ChangeCity()">
            <option>--请选择--</option>
            <option>北京市</option>
            <option>深圳市</option>
            <option>广州市</option>
            <option>杭州市</option>
            <option>西安市</option>
        </select>
        </p>
        <p>城市:        
        <select name="optCity" size="1">
            <option>--请选择--</option>
        </select>
        </p>
    </form></body></html>

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