js实现QQ面板拖拽效果（慕课网DOM事件探秘）（全）

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";}

loginState.onclick = function () {  stateList.style.display = "block";}document.onclick = function () {    stateList.style.display = "none";}

lis[i].onclick = function () {  stateList.style.display = "none";}loginState.onclick = function () {  stateList.style.display = "block";}

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";}

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;}