javascript - Get url from iframe and onclick modify the address -

i'm trying find way url iframe , using javascript modify link , move page. basicly address in iframe "http://www.somthing.com/12/somt/arr_1.htm", using javascript want remove last 5 character (leaving "http://www.somthing.com/12/somt/arr_") , add next logical number (making link "http://www.somthing.com/12/somt/arr__2.htm").

so far have this.

    <script language="javascript" type="text/javascript">     function urlgen(f){                        var i1 = document.getelementbyid("iframe_id").contentwindow.location.href;                        var i2 = "1.htm";                        var i3 = "2.htm";                        var newurl = i1 - i2 + i3                        f.action = i1 - i2 + i3                        return i1 - i2 + i3;                        } </script> 

so based on understand said should this? should this? (keep in mind i'm forest gump of javascript... "i'm not smart man know java is")

    <script language="javascript" type="text/javascript">     function urlgen(f){                        var i1 = document.getelementbyid("iframe_id").contentwindow.location.href = newurl;                        newurl = il.slice(0, -5);                        var i3 = "2.htm";                         f.action = newurl + i3                        } </script> 

try regular expression match

var i1 = "http://www.somthing.com/12/somt/arr_41.htm";    s = i1.replace(/\d+\.htm$/, function(attr) {    return attr.replace(/\d+/, function(val) {      return parseint(val,10) + 1;    });  });      alert(s);

this change string ends in x.htm (where x digit) in same string x+1 in place of x (adapted https://stackoverflow.com/a/1742841).