Add Leading Zero To Hours In Clock?

I am trying to edit one small thing in the javascript below but cannot get it to work correctly

What I am wanting to do is have the time with a 0 before the hour all the time except for 10, 11 or 12 o clock (e.g 09:00) I tried adding the following code it works but only for AM time and not PM time: -

// Pad the Hours with leading zeros, if required
currentHours = ( currentHours < 10 ? "0" : "" ) + currentHours;
Heres the code:
function init ( )
{
timeDisplay = document.createTextNode ( "" );

[Code]....