请教一个关于调用函数的问题!
function   setSubjectText(){

if(trim(document.form.radiobutton.value)   ==   " ")   {
        alert( "请选择交易类型 ");

        return   false;
}  
}


<form   method= "POST "   action= "save_product.asp "   name= "form "   >
    <input   type= "radio "   name= "radiobutton "   value= " ">
    <INPUT   class=subbutton   style= "WIDTH:   160px "       onclick=javascript:setSubjectText()   type=button   value=一切完成，我要发布！   name=Post>
</form>
  为什么弹不出 "请选择交易类型 "这个对话框呢?请帮忙分析一下.

------解决方案--------------------
<script language= "javascript ">
function setSubjectText(){
var str;
str = false;
for(i=0;i <form.radiobutton.length;i++)
{
if(form.radiobutton[i].checked==true)
{
str = true;
break;
}
}
if(!str)
{
alert( "请选择交易类型 ");
return false;
}
}

</script>

<form method= "POST " action= "save_product.asp " name= "form " >
<input type= "radio " name= "radiobutton " value= " ">
<input type= "radio " name= "radiobutton " value= " ">
<input type= "radio " name= "radiobutton " value= " ">
<INPUT class=subbutton style= "WIDTH: 160px " onclick=javascript:setSubjectText() type=button value=一切完成，我要发布！ name=Post>
</form>