js拖动div当鼠标移动时整个div也相应的移动_javascript技巧

$("#McreateUserGroup").mousedown(function(e){
var flag = true;
e = e||event;
var $dialog_createUserGroup = $("#dialog_createUserGroup");
var LEFT = e.clientX - parseInt($dialog_createUserGroup.css("left")),
TOP = e.clientY - parseInt($dialog_createUserGroup.css("top"));
$(document).mousemove(function (e) {
e = e || event;
if (flag) {
$dialog_createUserGroup.css({
"left": e.clientX - LEFT + "px",
"top": e.clientY - TOP + "px"
});
}
});
$(document).mouseup(function (e) {
flag = false;
});
});