JavaScript实现触摸移动功能

js»¬¶¯´¥ÆÁʼþ¼àÌý function span_move_fun(){
 var span = document.getElementById("move_k");
 var span_left = $(span).offset().left;
 var span_top = $(span).offset().top;
 var start_left = $(span).offset().left;
 var start_top = $(span).offset().top;
 span.addEventListener('touchstart', function(event) {
   event.preventDefault();
   if (event.targetTouches.length == 1) {
          var touch = event.targetTouches[0];
          span.style.position = "absolute";
    span_top = $(this).offset().top;
    span_left = $(this).offset().left;
    start_top = touch.pageY
    start_left = touch.pageX
          var left = parseFloat(touch.pageX - start_left + span_left-30);
          var top = parseFloat(touch.pageY - start_top + span_top-73);
    span.style.left = String(left) + 'px';
    span.style.top = String(top) + 'px';
         }
     });
     span.addEventListener('touchmove', function(event) {
   event.preventDefault();
   if (event.targetTouches.length == 1) {
    var touch = event.targetTouches[0];
    span.style.position = "absolute";
    var left = parseFloat(touch.pageX - start_left + span_left-30);
          var top = parseFloat(touch.pageY - start_top + span_top-73);
    span.style.left = String(left) + 'px';
    span.style.top = String(top) + 'px';