JavaScript中绑定事件的三种方式及去除绑定

<input type="button" onclick="func();">

<select name="xueli" >
 <option value="">请选择学历</option>
 <option value="大学" >大学</option>
 <option value="中学">中学</option>
 <option value="初中">初中</option> 
 <option value="小学">小学</option> 
</select>
<form action="">
 <p>Email:<input type="text" name="email">
  姓名：<input type="text" name="ming" >
 </p>
</form>

document.getElementsByTagName('select')[0].onclick= function (){
  alert('嘻嘻');
 }
document.getElementsByName('email')[0].onblur=function (){
 alert('哈哈哈');
}

window.onload = function(){
 var d = document.getElementById('school');
 function fn1(){
  alert('hello');
 }
 function fn2(){
  alert('world');
 }
 d.onclick = fn1;//赋值操作 最终显示fn2
 d.onclick = fn2;
}

//错误写法1
window.onload = function(){
 var d = document.getElementById('school');
 function fn1(){//this此时指向window
  this.style.background = 'blue';
 }
 function fn2(){//this此时指向window
  this.style.background = 'red';
 }
 //写一个匿名函数
 //最终的出现错误
 d.onclick = function (){
  fn1();
  fn2();
  //fn1 fn2是属性window的 实际上是这样 window.fn1() window.fn2()
  
  
 }
}

window.onload = function(){
 var d = document.getElementById('school');
 d.fn1 = function (){//fn1是d的属性 最终this此时指向DOM对象
  this.style.background = 'blue';
 }
 d.fn2 = function (){//this此时指向DOM对象
  this.style.background = 'red';
 }
 
 //匿名函数 调用上面两个函数
 d.onclick = function (){
  this.fn1();
  this.fn2();
 }
}

window.onload = function(){
 var d = document.getElementById('school');
 //达到了一次绑定两个函数
 d.addEventListener('click',function () {alert('blue');this.style.background ='blue'});
 d.addEventListener('click',function () {alert('red');this.style.background ='red'});
 
}

var fn1 = function () {alert('blue');this.style.background ='blue'};
var fn2 = function () {alert('red');this.style.background ='red'};
 
function adde(){
  var d = document.getElementById('school');
  d.addEventListener('click',fn1);
  d.addEventListener('click',fn2);
 }
function reme(){
 var d = document.getElementById('school');
 /https://img.qb5200.com/download-x/d.removeEventListener('click',fn1);//只剩fn1
 d.removeEventListener('click',fn2);
}

<div id="school">
 
 </div>
 <input type="button" value="加事件" onclick="adde();">
 <input type="button" value="减事件" onclick="reme();">

var fn1 = function () {alert('blue');this.style.background ='blue'};
var fn2 = function () {alert('red');this.style.background ='red'};
 
function adde(){
  var d = document.getElementById('school');
  // IE6,7是后绑定的事件先发生
  d.attachEvent('onclick',fn1);
  d.attachEvent('onclick',fn2); //fn2先发生
 }
function reme(){
 var d = document.getElementById('school');
 /https://img.qb5200.com/download-x/d.deltachEvent('click',fn1);//只剩fn1
 d.deltachEvent('click',fn2);
}