js获取select改变事件

js获取select改变事件onchage前的值 和 onclick事件

<select id="wupin_id" name="wupin_id" onclick="saveLast()" onchange="changeForm(this.value)" >
<option value="0" selected>请选择您要使用的设备类型</option>
<option value="001">惠普扫描仪G5590</option>
<option value="002">惠普扫描仪G2410</option>
<option value="003">惠普扫描仪G3110</option>
</select>

<script>
var lastIndex,lastValue;

function saveLast(){
var select = document.getElementById("wupin_id");

lastIndex = select.selectedIndex;
var midValue = select.options[lastIndex].value;
//var text = select.options[index].text;
if(midValue!="0"){
lastIndex = select.selectedIndex;
lastValue = select.options[lastIndex].value;
}
}

应用：
function changeForm(val){
var obj=document.getElementById("wupin_id");
var tr01=document.getElementById("tr01").value;
var flag=document.getElementById("saverk").disabled;
var flag2=document.getElementById("tr01").disabled;
if(val!="0" && flag2==true){
document.getElementById("tr01").disabled=false;
document.getElementById("tr01").focus();
}
if(val!="0" && tr01!="" && flag!=true){
alert("请先保存入库，再进行其他型号物品的扫描录入！");
obj.options[lastIndex].selected=true; //加载用户改变以前的选中的值
document.getElementById("saverk").focus();
}

}