I want to copy present address value to permanent address using checkbox having multiple rows and each row has the checkbox

these are my javascript codes

 function copyaddress(f){
if(f.ADDTYPE.checked==true)
    {

        f.txtPerBuildNo.value=f.txtPreBuildNo.value;
        f.txtPerBuildNo.readOnly=true;
        f.txtPerArea.value=f.txtPreArea.value;
        f.txtPerArea.readOnly=true;
    }

else
    {
        f.txtPerBuildNo.value="";
        f.txtPerBuildNo.readOnly=false;
        f.txtPerArea.value="";
        f.txtPerArea.readOnly=false;
    }
}

the codes will copy present adrress to permanent address when the particular checkbox is clicked