getTimeFromMillis.js

// converts milliseconds to '3:45' or if hours > 0, '2:01:23'
var getTimeFromMillis = function( ms ) 
{
  var seconds = ':' + twoDigit( ~~( ( ms / 1000 ) % 60 ) ),
      minutes = ~~( ( ms / ( 1000 * 60 ) ) % 60 ),
      hours   = ~~( ( ms / ( 1000 * 60 * 60 ) ) );

  function twoDigit( n ) { return n < 10 ? '0' + n : n; }

  return hours > 0 ? hours + ':' + twoDigit( minutes ) + seconds : minutes + seconds;
};