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;});