How to automatically select all options in select

I want to get a javascript Program It is used to select all the options in the SELECT statement, and then place the program into the onsubmit of the form. This way, all options are automatically selected in the commit statement, which can also be received. How can I write this section of JavaScript?
Linux_boot ---------------------------------------------------------------

<Select id = A1 multiple>
<Option> 123 </option>
<Option> 456 </option>
<Option> 789 </option>
</SELECT>
<Input type = button value = change onclick = "for (I = 0; I <a1.options. length; I ++) a1.options (I). Selected = true">
---------------------------------------------------------------

Ah ~~ Right? ... You select the selected value through form
An array is submitted. You don't need to select ......

If you want to process it separately, split the array.
---------------------------------------------------------------



<Form onsubmit = ifsubmit name = FRM>
.........
<Select id = select2 multiple>
<Option> 123 </option>
<Option> 456 </option>
<Option> 789 </option>
</SELECT>

</Form>
<SCRIPT>
Function ifsubmit (){
VaR objsel = FRM. Select;
VaR intlen = objsel. length;
For (VAR I = 0; I <intlen; I ++)
Objsel [I]. Selected = true;
FRM. Submit ();
}
</SCRIPT>
---------------------------------------------------------------

<Option> 456 </option>
<Option> 789 </option>
</SELECT>

</Form>
<SCRIPT>
Function ifsubmit (){
VaR objsel = FRM. Select;
VaR intlen = objsel. length;
For (VAR I = 0; I <intlen; I ++)
Objsel [I]. Selected = true;

}
</SCRIPT>