Detect double tap on ipad or iphone screen using javascript

This could be used for a double tap or a double click. In pure javascript:

var mylatesttap;
function doubletap() {

   var now = new Date().getTime();
   var timesince = now - mylatesttap;
   if((timesince < 600) && (timesince > 0)){

    // double tap   

   }else{
            // too much time to be a doubletap
         }

   mylatesttap = new Date().getTime();

}