Guys

I need to determine which textbox to return a value to using javascript.

In the code below, I need the value 'premtype' to be either prem or alt_prem depending on the radio button selected. I just can't seem to figure out how to pass the variable into the 'document.frm.variablehere.value' statement:

Code:
//check if renewal premium or alternative renewal premium has been chosen....

if (document.frm.choice[0].checked)//renewal premium
	{
		total = document.frm.prem.value
		premtype = "prem"
             }
else
	{//alt renewal premium
		total = document.frm.alt_prem.value
		premtype = "alt_prem"
	}	

//work out premiums.......		
	if (stmt == true)//checkbox checked....
		{
			//calculate the new premium amount
			total = parseFloat(total) + parseFloat(changeBy);
			//populate premium field
			document.frm.premtype.value = Math.abs(total).toFixed(2);
		}
	else//checkbox unchecked....
		{
			//calculate the new premium amount
			total = parseFloat(total) - parseFloat(changeBy);
			//populate 'prem' field
			document.frm.premtype.value = Math.abs(total).toFixed(2);			
		}

I hope this makes sense!

Cheers