js实现滑动触屏事件监听的方法

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';
 }
 });
  span.addEventListener('touchend', function(event) {
  var touch = event.changedTouches[0];
  if(parseFloat(touch.pageX - start_left + span_left-30) <= -5 || parseFloat(touch.pageX - start_left + span_left-30) >= 620 || parseFloat(touch.pageY - start_top + span_top-73) <= -38 || parseFloat(touch.pageY - start_top + span_top-73) >= 587){
  span.style.left = String(span_left-30) + 'px';
 span.style.top = String(span_top-73) + 'px';
  }
 event.stopPropagation();
 });
}

document.getElementsByTagName_r('body')[0].addEventListener('touchstart',function(e){
  nStartY = e.targetTouches[0].pageY;
  nStartX = e.targetTouches[0].pageX;
});
document.getElementsByTagName_r('body')[0].addEventListener('touchend',function(e){
  nChangY = e.changedTouches[0].pageY;
  nChangX = e.changedTouches[0].pageX;
});