Select触发事件

 案例1:

<script type="text/JavaScript">
       function gradeChange(){
        var objS = document.getElementById("weather-select");
        var valueStr = objS.options[objS.selectedIndex].value;
        alert(valueStr);
       }
</script>

<select id="weather-select" style="width:100%;" onchange="gradeChange()">
  <optgroup label="港澳台、直辖市">
    <option value="beijing" selected>北京</option>
    <option value="shanghai">上海</option>
    <option value="tianjin">天津</option>
      <optgroup label="xxx">
        <option value="zhongqing">重庆</option>
        <option value="xianggang">香港</option>
      </optgroup>
    <option value="aomen">澳门</option>
    <option value="taibei">台北</option>
  </optgroup>
</select>

案例2:

js代码：

<script type="text/javascript">
    var setitem = new Array(4);
    for(i=0;i<4;i++){
        setitem[i] = new Array();
    }
    setitem[0][0] = new Option("请选择"," ");
    setitem[1][0] = new Option("小学数学","小学数学");
    setitem[1][1] = new Option("小学语文","小学语文");
    setitem[1][2] = new Option("小学英语","小学英语");

    setitem[2][0] = new Option("中学数学","中学数学");
    setitem[2][1] = new Option("中学语文","中学语文");
    setitem[2][2] = new Option("中学英语","中学英语");
    setitem[2][3] = new Option("中学政治","中学政治");

    setitem[3][0] = new Option("大学数学","大学数学");
    setitem[3][1] = new Option("大学语文","大学语文");
    setitem[3][2] = new Option("大学英语","大学英语");
    setitem[3][3] = new Option("大学英语","大学英语");
    setitem[3][4] = new Option("大学物理","大学物理");
    setitem[3][5] = new Option("大学政治","大学政治");

    function onS1change(index){
      var sell1 = document.getElementById("sell1");
       sell1.length = 0;//删除所有选项
       for(i=0;i<setitem[index].length;i++){
           sell1.options[i] = setitem[index][i];
       }

       sell1.options[0].select = true;

    }
    function onS2change(str1,str2){
      alert(str1+" "+str2);
    }

</script>

<form name="form1" id="form1">
	<label>您的身份是
        <select name="sell" onchange="onS1change(this.value)">
          <option value="0">请选择</option>
          <option value="1">小学生</option>
          <option value="2">中学生</option>
          <option value="3">大学生</option>
        </select>
	</label>

	<label>您最喜欢的科目

        <select id="sell1" ">

        </select>
 	</label>
    <br/>
    <input type="submit" name="Submit" onclick="onS2change(sell.value,sell1.value)">
</form>

注意点： str1是描述，str2是值

 new Option("str1","str2")

 <option value="这里是str2">这里是str1</option>

获取value：

var sell = document.getElementById("sell");
alert(sell.options[sell.options.selectedIndex].value);

获取text

var sell = document.getElementById("sell");
alert(sell.options[sell.options.selectedIndex].text);