JavaScript 事件对内存和性能的影响

<ul id="parent-list">
 <li id="list-1">List 1</li>
 <li id="list-2">List 2</li>
 <li id="list-3">List 3</li>
 <li id="list-4">List 4</li>
 <li id="list-5">List 5</li>
</ul>

// 方法一
var list1 = document.getElementById("list-1");
list1.addEventListener("click",function(){
 alert(this.firstChild.nodeValue);
},false);
var list2 = document.getElementById("list-2");
list2.addEventListener("click", function() {
 alert(this.firstChild.nodeValue);
}, false);
var list3 = document.getElementById("list-3");
list3.addEventListener("click", function() {
 alert(this.firstChild.nodeValue);
}, false);
var list4 = document.getElementById("list-4");
list4.addEventListener("click", function() {
 alert(this.firstChild.nodeValue);
}, false);
var list5 = document.getElementById("list-5");
list5.addEventListener("click", function() {
 alert(this.firstChild.nodeValue);
}, false);
// 方法二
var parentList = document.getElementById("parent-list");
parentList.addEventListener("click",function(){
 var target = event.target;
 if(target.nodeName.toLowerCase() === "li"){
 alert(target.firstChild.nodeValue);
 }
},false);

// 方法二
var parentList = document.getElementById("parent-list");
parentList.addEventListener("click",function(){
 var target = event.target;
 if(target.nodeName.toLowerCase() === "li"){
 switch(target.id){
  case "list-1":
  alert("学的越多，越觉得自己无知！");
  break;
  case "list-2":
  alert("爱是一种艺术！");
  break;
  case "list-3":
  target.innerHTML = "呵呵，我改了啊！";
  break;
  case "list-4":
  target.style.background = "#aaa";
  break;
  case "list-5":
  target.style.color = "red";
  target.style.fontSize = "2em";
  break;
  default:
  break;
 }
 }
},false);

<button id="button">提交</button>
var button = document.getElementById("button");
button.onclick = function(){
 // 提交某个表单的操作代码
 button.onclick = null; // 移除事件处理程序
 event.target.firstChild.nodeValue = "提交中。。。";
};