这个对象如何传递呀

Question

<form name=form1>
<input name="textfield" type="text"  onBlur="num(this)" >    
<script language=javascript>
 function num(obj,myMaxLength,conclName)
    {
obj.value = "";
}
</script>
</form>

Answer 1

<form name=form1><input name="textfield" type="text"  onBlur="num('textfield')" >    
<script language=javascript>
function num(str,myMaxLength,conclName)
    {
    form1.elements[str].value="";
}
</script>
</form>

Answer 2

<form name=form1><input name="textfield" type="text"  onBlur="num('textfield')" >    
<script language=javascript>
function num(str,myMaxLength,conclName)
    {
    form1.elements[conclName].value="";
}
</script>
</form>