代码：

function drag(t,p){ var point = p || null, target = t || null, resultX = 0, resultY = 0; (!point)? point = target : ''; //如果没有拖动点，则拖动点默认为整个别拖动元素 function getPos(t){ var offsetLeft = 0, offsetTop = 0, offsetParent = t; while(offsetParent){ offsetLeft+=offsetParent.offsetLeft; offsetTop+=offsetParent.offsetTop; offsetParent = offsetParent.offsetParent; } return {'top':offsetTop,'left':offsetLeft}; } function core(){ var width = document.body.clientWidth || document.documentElement.clientWidth, height = document.body.clientHeight || document.documentElement.clientHeight; maxWidth = width - target.offsetWidth, maxHeight = height - target.offsetHeight; (resultX >= maxWidth)? target.style.left = maxWidth+'px' : (resultX > 0)?target.style.left = resultX +'px': ''; //重置默认位置。 (resultY >= maxHeight)? target.style.top = maxHeight +'px' : (resultY > 0)?target.style.top = resultY +'px':''; //重置默认位置。 point.onmousedown=function(e){ var e = e || window.event, coordX = e.clientX, coordY = e.clientY, posX = getPos(target).left, posY = getPos(target).top; point.setCapture && point.setCapture(); //将Mouse事件锁定到指定元素上。 document.onmousemove=function(e){ var ev = e || window.event, moveX = ev.clientX, moveY = ev.clientY; resultX = moveX - (coordX - posX); //结果值是坐标点减去被拖动元素距离浏览器左侧的边距 resultY = moveY - (coordY - posY); (resultX > 0 )?((resultX < maxWidth)?target.style.left = resultX+'px' : target.style.left = maxWidth+'px') : target.style.left = '0px'; (resultY > 0 )?((resultY < maxHeight)?target.style.top = resultY+'px' : target.style.top = maxHeight+'px') : target.style.top = '0px'; ev.stopPropagation && ev.stopPropagation(); ev.preventDefault; ev.returnValue = false; ev.cancelBubble = true; }; }; document.onmouseup=function(){ // 解决拖动时，当鼠标指向的DOM对象非拖动点元素时，无法触发拖动点的onmousedown的BUG。 document.onmousemove = null; point.releaseCapture && point.releaseCapture(); // 将Mouse事件从指定元素上移除。 }; point.onmouseup=function(e){ var e = e || window.event; document.onmousemove = null; point.releaseCapture && point.releaseCapture(); }; } core(); window.onresize = core; }

使用方式：

drag(t,p) /* * 说明 * t 表示被拖动的元素 * p 表示拖动点 */ // 注意：如果省略拖动点，默认可拖动的区域是整个被拖动元素