这个代码里按回车的时候为什么总是有从主板发声?

完整代码如下
<html>
<head></head>
<boay>
<form name ="frm1" method="POST">
<input type="text" name="txt1"  onKeyPress="turnToNext(this)"/>
<input type="text" name="txt2"  onKeyPress="turnToNext(this)"/>
<input type="text" name="txt3"  onKeyPress="turnToNext(this)"/>
<input type="text" name="txt4"  onKeyPress="turnToNext(this)"/>
<input type="text" name="txt5"  onKeyPress="turnToNext(this)"/>
</form>
<SCRIPT LANGUAGE="Javascript">
function turnToNext(obj){
   if(window.event.keyCode==13){
     var name=obj.name
var Length=window.document.frm1.length
var i=0
for(i=0 ;i<Length;i++){
     var obj2=window.document.frm1.elements[i]
      if(name==obj2.name){
alert(name+"  "+obj2.name)
obj2=window.document.frm1.elements[i+1]
        obj2.focus();
//
        break;        
}
}}
}
</SCRIPT>
</body>
</html>