javascript countdown timer

Hi all,

I am missing something here. . . I am trying to make a 10 minute countdown timer. I found some code and modified it so it counts down from 10 minutes like I wanted, but now I have two problems.
1. I want it to stop at 0, and
2. I want a popup box when it gets there.

I have tried all sorts of combinations, and I cannot seem to figure out how to do this. can anyone point me in the right direction?

<SCRIPT TYPE="text/javascript" LANGUAGE="Javascript">

/* chrono.js

 * Role : Simulate a stopwatch with display controls

 * Projet : JsLib

 * Author : Etienne CHEVILLARD (echevillard@users.sourceforge.net)

 * Version : 1.3

 * Creation : 25/04/2001

 * Mise a jour : 23/02/2005

 */


// --- Global Variables ---


// variables defineing the lenth of time

var chrono_demarre=false; //does the timer start on page load

var chrono_ecoule=600000; //the starting time for the timer

var chrono_depart=0; //these two variables control the flow of the timer - this is the starting time

var chrono_dernier=0; // and this is the ending time. These are subtracted to count down or up.


// set the variables for dynamic display

var chrono_champ;

var chrono_timeout;


//  ---Functions---


// is the stopwatch running? aka has the stop button been pushed

function actifChrono() {

  return (chrono_demarre);

} // finish actifChrono()


// stop the stopwatch

function arreterChrono() {

  if (chrono_demarre) {

    chrono_dernier=(new Date()).getTime();

    chrono_ecoule-=(chrono_dernier-chrono_depart);

    chrono_demarre=false;

  }

  return true;

} // finish arreterChrono()


// activate dynamic display of the time mesurment

function chargerChronoDyna(champ) {

  if (champ)

    chrono_champ=eval(champ);

  chrono_champ.value=tempsChrono();

      

  chrono_timeout=window.setTimeout("chargerChronoDyna()", 10);

  return true;

} // fin chargerChronoDyna(champ)


// display of time measurment previously activated

function dechargerChronoDyna() {

  window.clearTimeout(chrono_timeout);

  return true;

} // fin dechargerChronoDyna()


// start the stopwatch

function demarrerChrono() {

  if (!chrono_demarre) {

    chrono_depart=(new Date()).getTime();

    chrono_demarre=true;

  }


  return true;

} // fin demarrerChrono()


// reset the stopwatch to default time

function RAZChrono() {

  if (!chrono_demarre) {

    chrono_ecoule=600000;

    chrono_depart=0;

    chrono_dernier=0;

  }

  return true;

} // finish RAZChrono()


// format the display time (if needed HH:)MM:SS:CC

function tempsChrono() {

  var cnow;

  if (chrono_demarre) {

    chrono_dernier=(new Date()).getTime();

    cnow=new Date(chrono_ecoule-(chrono_dernier-chrono_depart));

  } else {

    cnow=new Date(chrono_ecoule);

  }

  var ch=parseInt(cnow.getHours()) - 1; //if needed

  var cm=cnow.getMinutes();

  var cs=cnow.getSeconds();

  var cc=parseInt(cnow.getMilliseconds()/10);

  if (cc<10) cc="0"+cc;

  if (cs<10) cs="0"+cs;

  if (cm<10) cm="0"+cm;

  return (cm+":"+cs+":"+cc);


} // finish tempsChrono()

    

<BODY onLoad="chargerChronoDyna('document.f.t')"

    onUnload="dechargerChronoDyna()">

 


  

      <FORM ACTION="GET" NAME="f">

        <INPUT NAME="t" TYPE=TEXT VALUE="0:00:00:00" SIZE=12> 

        <INPUT TYPE=BUTTON VALUE="start/stop"

        onClick="if (actifChrono()) arreterChrono(); else demarrerChrono();"> 

        <INPUT TYPE=BUTTON VALUE="Reseto" onClick="RAZChrono();">

      </FORM>

</SCRIPT>

<html> <head> <script type="text/javascript"> var mins = 10; var secs = 0; var timer; function start(){ timer = setInterval('update()', 1000); } function update(){ var timeField = document.getElementById('time'); if(secs == 0){ if(mins == 0){ timeField.innerHTML = 'Time's up!'; clearInterval(timer); alert('Time's up'); return; } mins--; secs = 59; } else { secs--; } if(secs<10){ timeField.innerHTML = 'Time left: ' + mins + ':0' + secs; } else { timeField.innerHTML = 'Time left: ' + mins + ':' + secs; } } </script> </head> <body onload="start();"> <div id="time" > </div> </body> </html>

if(secs == 0){ if(mins == 0){ timeField.innerHTML = 'Time's up!'; clearInterval(timer); alert('Time's up'); return;