* { margin: 0; padding: 0;}html,body { width: 100%; height: 100%;}#div1 { width: 50px; height: 50px; background: cyan; position: absolute;}

var div1 = document.querySelector('#div1');//限制最大寬高，不讓滑塊出去var maxW = document.body.clientWidth - div1.offsetWidth;var maxH = document.body.clientHeight - div1.offsetHeight;//手指觸摸開始，記錄div的初始位置div1.addEventListener('touchstart', function(e) { var ev = e || window.event; var touch = ev.targetTouches[0]; oL = touch.clientX - div1.offsetLeft; oT = touch.clientY - div1.offsetTop; document.addEventListener("touchmove", defaultEvent, false);});//觸摸中的，位置記錄div1.addEventListener('touchmove', function(e) { var ev = e || window.event; var touch = ev.targetTouches[0]; var oLeft = touch.clientX - oL; var oTop = touch.clientY - oT; if(oLeft < 0) { oLeft = 0; } else if(oLeft >= maxW) { oLeft = maxW; } if(oTop < 0) { oTop = 0; } else if(oTop >= maxH) { oTop = maxH; } div1.style.left = oLeft + 'px'; div1.style.top = oTop + 'px';});//觸摸結束時的處理div1.addEventListener('touchend', function() { document.removeEventListener("touchmove", defaultEvent);});//阻止默認事件function defaultEvent(e) { e.preventDefault();}