JavaScript DOM events (notes)_javascript skills

Chapter 1 Event Flow

1-1. Event bubbling: The event is initially received by the most specific element (the node with the deepest nesting level in the document);
Then propagate up to the least specific node (document) step by step;
1-2. Event capture: Less specific nodes should receive events earlier, while the most specific nodes should receive events last;

Chapter 2 Event Handler

2-1 HTML event handler
//Disadvantages: HTML and JS code are tightly coupled together;

<input type="button" value="按钮" onclick="showMessage()">

2-2 DOM level 0 event handler

//The more traditional way: assign a function to the handler attribute of an event, which is more commonly used;
//Advantages: Simple/cross-browser;

<input type="button" value="按钮" id="btn2">
<script>
  var btn2 = document.getElementById('btn2'); //取得btn2按钮对象;
  btn2.onclick = function () {        //给btn2添加onclick属性;
    alert('这是通过DOM0级添加的事件!');
  }
  btn2.onclick=null;             //删除onclick属性;
</script>

2-3 DOM2 level event handler

//DOM2 level events define two methods: for handling the operations of specifying and deleting event handlers;
//addEventListener() and removeEventListner();
//Receive three parameters: event name to be processed/event processing function and Boolean value;
//It doesn’t work in IE8;

<input type="button" value="按钮" id="btn3">
<script>
  var btn3 = document.getElementById('btn3');
  btn3.addEventListener('click',showMessage,false);    //添加事件程序;
  btn3.addEventListener('click',function(){        //添加多个事件程序;
    alert(this.value);
  },false);
  btn3.removeEventListener('click',showMessage,false);  //删除事件程序;
</script>

2-4 IE event handler and cross-browser

//Receives two parameters: event processing function name and event processing function

<script>
   var btn3 = document.getElementById('btn3');
   btn3.attachEvent('onclick',showMessage);      //添加事件;
   btn3.detachEvent('onclick',showMessage);      //删除事件;
</script>

>2. Browser compatible

//将添加和删除事件处理程序封装到对象中并赋值给变量'eventUtil';
var eventUtil = {
  //添加句柄
  addHandler:function(element,type,handler){
    //判断DOM2级事件处理程序;
    if(element.addEventListener){  
      element.addEventListener(type,handler,false);
    //判断IE浏览器;
    }else if(element.attachEvent){
      element.attachEvent("on"+type,handler);
    //使用DOM0级事件处理程序;
    }else{
      element['on'+type] = handler;
    }
  };
  //删除句柄
  removeHandler:function(element,type,handler){
    //判断DOM2级事件处理程序;
    if(element.removeEventListener){  
      element.removeEventListener(type,handler,false);
    //判断IE浏览器;
    }else if(element.detachEvent){
      element.detachEvent("on"+type,handler);
    //使用DOM0级事件处理程序;
    }else{
      element['on'+type] = null;
    };
  };
};
//跨浏览器添加事件处理程序;
eventUtil.addHandler(btn3,'click',showMessage);

Chapter 3 Event Object

3-1 Event objects in DOM

//When an event on the DOM is triggered, an object ==event will be generated;

>1.type == Get event type;
>2.target == Get event target;
>3.stopPropagation() == Stop event bubbling;
>4.preventDefault() == Default behavior of preventing events;

function showMes(event){
  alert(event.type);          //onclick;点击事件;
  alert(event.target.nodeName);  　　//INPUT;input按钮被触发;
  event.stopPropagation();      //停止事件冒泡;
}
<a href="event.html" onclick="stopGoto();">跳转</a>
function stopGoto(event){
  event.preventDefault();　　　　　　　//阻止默认行为;
}

3-2 Event objects in IE

>1.type == Same as above;
>2.srcElement attribute == Get event target;
>3.cancleBubble attribute == Prevent bubbling; set true to prevent bubbling, false to not prevent bubbling;
>4.returnValue attribute == Default behavior for blocking events;

function showMes(event){
  //非IE用event,IE8以下用window.event;
  event = event || window.event;  
  //事件目标兼容;
  var ele = event.target || event.srcElement;
  //兼容阻止事件冒泡;
  if(event.stopPropagation){
    event.stopPropagation();
  }else{
    event.cancleBubble();
  };
  //兼容取消事件默认行为;
  if(event.preventDefault){
    event.preventDefault();
  }else{
    event.returnValue = false;
  }
}

Chapter 4 QQ Panel Drag Effect

>1. Encapsulate the Class method

function getClass(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;
}

>2. Encapsulate drag and drop function

window.onload = drag;
function drag(){
  var oTitle = getClass('login_logo_webqq','loginPanel')[0];  
  //拖拽
  oTitle.onmousedown = fnDown;
  //关闭弹窗
  var oClose = document.getElementById('ui_boxyClose');
  oClose.onclick = function(){
    document.getElementById('loginPanel').style.display = 'none';
  }
  //切换状态
  var loginState = document.getElementById('loginstate'),
    stateList = document.getElementById('loginStatePanel'),
    lis = stateList.getElementsByTagName('li'),
    stateTxt = document.getElementById('login2qq_state_txt'),
    loginStateShow = document.getElementById('login-state_show');
  loginState.onclick = function(e){
    //阻止冒泡到document使ul隐藏;
    e = e || window.event;
    if(e.stopPropagation){
      e.stopPropagation();
    }esle{
      e.cancleBubble = true;
    }
    stateList.style.display = "block";
  }
  //鼠标滑过/离开和点击状态列表时
  for(var i=0,i<lis.length,i++){
    lis[i].onmouseover = function(){
      this.style.background = "#567";
    }
    lis[i].onmouseout = function(){
      this.style.background = "#fff";
    }
    lis[i].onclick = function(e){
      //阻止冒泡到loginState使stateList显示;
      e = e || window.event;
      if(e.stopPropagation){
        e.stopPropagation();
      }esle{
        e.cancleBubble = true;
      }
      var id = this.id;
      stateList.style.display = "none";
      stateTxt.innerHTML = getClass('stateSelect_text',id)[0].innerHTML;
      loginStateShow.className = '';
      loginStateShow.className = 'login-state-show '+id;
    }
  }
  document.onclick = function(){
    stateList.style.display = "none";
  }
}
//鼠标按下事件;
function fnDown(event){
  event = event || window.event;
  var oDrag = document.getElementById('loginPanel'),
      //鼠标按下时,鼠标和面板之间的距离;
      disX = event.clientX - oDrag.offsetLeft,
      disY = event.clientY - oDrag.offsetTop;
  //移动
  document.onmouseover = function(event){
    event = event || window.event;
    fnMove(event,disX,disY);
  }
  //释放鼠标
 document.onmouseup = function(){
  document.onmouseover = null;
  document.onmouseup = null;
  }
}
//鼠标移动事件;
function fnMove (e,posX,posY){
  var oDrag = document.getElementById('loginPanel'),
      l = e.clientX-posX,
      t = e.clientY-posY,
      winW = document.documentElement.clientWidth || document.body.clientWidth,
   winH = document.documentElement.clientHeight || document.body.clientHeight;
   maxW = winW-oDrag.offsetWidth,
   maxH = winH-oDrag.offsetHeight;
 if(l<0){
   l = 0;
 }else if(l>maxW){
   l = maxW;
 }
 if(t<0){
   t = 0;
 }else if(t>maxH){
   t=maxH;
 }
  oDrag.style.left = l+'px';
  oDrag.style.top = t+'px';
}

Chapter 4 Lottery System

>1.Keyboard events

>>1.keyDown: Triggered when the user presses any key on the keyboard, and if the user holds down the key, this event will be triggered repeatedly;
>>2.keyPress: Triggered when the user presses a character key on the keyboard, and if the user presses and holds it, this event will be triggered repeatedly;
>>3.keyUp: Triggered when the user releases a key on the keyboard;

>2. Lottery procedure

var data = ['iPhone5','iPad','三星电脑','谢谢参与'],
    timer = null,
    flag = 0;
window.onload = function(){
  var play = document.getElementById('play'),
    stop = document.getElementById('stop');
  //(鼠标)开始抽奖
  play.onclick = palyFun;
  stop.onclick = stopFun;
  //(键盘Enter)开始抽奖
  document.onkeyup = function(event){
    event = event || window.event; 
    if(event.keyCode == 13){
      if(flag == 0){
        palyFun();
        flag = 1;
      }else{
        stopFun();
        flag = 0;
      }
    }
  }
}
function palyFun(){
  var title = document.getElementById('title'),
    play = document.getElementById('play');
  //清除之前的定时器,放置定时器重复;
  clearInterval(timer);
　　　　//设置定时器;
  timer = setInterval(function(){
    //随机数*数组元素个数=数组随机索引;
    var random = Math.floor(Math.random()*data.length);
    title.innerHTML = data[random];
  },50);
  play.style.background = "#999";
}
function stopFun(){
  clearInterval(timer);
  var paly = document.getElementById('play');
  paly.style.background = '#036';  
}