QQ面板拖拽（慕课网DOM事件探秘）（上）

function getByClass(clsName, parent) {
var oParent = parent ? document.getElementById(parent) : document,
eles = [],
elements = oParent.getElementsByTagName('*'); for (var i = 0, l = elements.length; i < l; i++) {
if (elements[i].className == clsName) {
eles.push(elements[i]);
}
}
return eles;
}window.onload = drag;function drag() {
var oTitle = getByClass("login_logo_webqq", "loginPanel")[0];
//拖页
oTitle.onmousedown = fnDown;
//关闭页面
var close = document.getElementById("ui_boxyClose");
close.onclick = winClose;
//切换状态
var loginState = document.getElementById("loginState");
var stateList = document.getElementById("loginStatePanel");
var lis = stateList.getElementsByTagName("li");
var stateTxt = document.getElementById("login2qq_state_txt");
var loginStateShow = document.getElementById("loginStateShow");
//点击显示下拉单
loginState.onclick = function (e) {
stateList.style.display = "block";
//阻止事件冒泡；
e = event || window.event;
if(e.stopPropagation){
e.stopPropagation();
}else{
e.cancelBubble = true;
}
};
//鼠标滑过,背景变色
for (var i = 0; i < lis.length; i++) {
lis[i].onmouseover = function () {
this.style.backgroundColor = "#888";
};
lis[i].onmouseout = function () {
this.style.backgroundColor = "#fff";
};
//鼠标点击，txt改变，图标改变
lis[i].onclick = function (e) {
stateList.style.display = "none";
//阻止事件冒泡
e = event || window.event;
if(typeof e.stopPropagation){
e.stopPropagation();
}else {
e.cancelBubble = true;
}
var id = this.id;
loginStateShow.className = "login-state-show "+id;
var text = getByClass("stateSelect_text",id)[0].innerHTML;
stateTxt.innerHTML = text;
} }
document.onclick = function () {
stateList.style.display = "none";
}
}function winClose() {
var box = document.getElementById("loginPanel");
box.style.display = "none";
}function fnDown(event) {
var event = event || window.event;
var oDrag = document.getElementById("loginPanel");
//光标按下时光标和面板之间的距离；
var disX = event.clientX - oDrag.offsetLeft;
var disY = event.clientY - oDrag.offsetTop;
//移动
document.onmousemove = function (event) {
event = event || window.event;
fnMove(event, disX, disY);
};
document.onmouseup = function () {
document.onmousemove = null;
document.onmouseup = null;
}
}function fnMove(event, posX, posY) {
var oDrag = document.getElementById("loginPanel");
var l = event.clientX - posX;
var t = event.clientY - posY;
var winW = document.documentElement.clientWidth;
var winH = document.documentElement.clientHeight;
var maxW = winW - oDrag.offsetWidth - 10;
var maxH = winH - oDrag.offsetHeight;
//当l=0时，窗口不能继续外移
if (l < 0) {
l = 0;
} else if (l > maxW) {
l = maxW;
} if (t < 10) {
t = 10;
} else if (t > maxH) {
t = maxH;
} oDrag.style.left = l + "px";
oDrag.style.top = t + "px";}