JavaScript 实现高级拖拽：setCapture 与 releaseCapture 详解

 
<script type="text/javascript">
<!-- 
window.onload=function(){
objDiv = document.getElementById('drag');
drag(objDiv);
}; 
function drag(dv){
dv.onmousedown=function(e){
var d=document;
e = e || window.event;
var x= e.layerX || e.offsetX;
var y= e.layerY || e.offsetY;
//设置捕获范围
if(dv.setCapture){
dv.setCapture();
}else if(window.captureEvents){
window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);
} 
d.onmousemove=function(e){
e= e || window.event;
if(!e.pageX)e.pageX=e.clientX;
if(!e.pageY)e.pageY=e.clientY;
var tx=e.pageX-x;
var ty=e.pageY-y;
dv.style.left=tx;
dv.style.top=ty;
}; 
d.onmouseup=function(){
//取消捕获范围
if(dv.releaseCapture){
dv.releaseCapture();
}else if(window.captureEvents){
window.captureEvents(Event.MOUSEMOVE|Event.MOUSEUP);
} 
//清除事件
d.onmousemove=null;
d.onmouseup=null;
}; 
}; 
} 
//--> 
</script>
<div id="drag" style="position:absolute;left:12px;top:24px;width:100;height:150;border:1px solid #000000;z-index:1;background:#eeeeee">drag me</div>

setCapture 的作用是指定触发对象方法的范围或作用域。

若不设置捕获，div 仅在当前窗口内触发；若设置捕获，则在整个浏览器范围内触发，允许将元素拖拽至浏览器外部。