JS实现select选中option触发事件操作示例

var vi = document.all['list'].length;
for(var i=0;i<vi;i++){
  document.form2.list(i).value; //form2是<form>的名称
}

‍‍<select id="pid" onchange="gradeChange()">
  <option grade="1" value="a">选项一</a>
  <option grade="2" value="b">选项二</a>
</select>
<script type="text/JavaScript">
    function gradeChange(){
    var objS = document.getElementById("pid");
    var grade = objS.options[objS.selectedIndex].grade;
    alert(grade);
    }
</script>

<select name="myselect" id="myselect">
  <option value="opt1">选项1</option>
  <option value="opt2">选项2</option>
  <option value="opt3">选项3</option>
</select>
$("#myselect").change(function(){
  var opt=$("#myselect").val();
  ...
});

<select id="test" name="">
 <option value="1">text1</option>
 <option value="2">text2</option>
</select>

var myselect=document.getElementById("test");

var index=myselect.selectedIndex;
// selectedIndex代表的是你所选中项的index

myselect.options[index].value;

myselect.options[index].text;

var options=$("#test option:selected");

alert(options.val());

alert(options.text());