原生JavaScript实现淘宝购物车核心逻辑

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
*{padding:0;margin:0;}
#list,p{list-style:none;width:600px;margin:0 auto;}
#list li {width:600px;height:50px;line-height:50px;margin-top:20px;font-size:20px;}
#list li input{width:60px;height:40px;line-height:40px;}
.highlight{color:red;font-size:30px;font-weight:bold;}
</style>
<script>
window.onload = function () {

 var oUl = $('list');
 var totalNumber = $('totalNum');
 var totalPrice = $('totalPrice');
 var mostExpensive = $('mostExpensive');
 var aLi = oUl.getElementsByTagName('li');
 var maxPrice = [0];

 for ( var i = 0; i < aLi.length; i++ ) {
 price(aLi[i]);
 }

 function price(oLi) {

 var aBtn = oLi.getElementsByTagName('input');
 var oStrong = oLi.getElementsByTagName('strong')[0];
 var oEm = oLi.getElementsByTagName('em')[0];
 var oSpan = oLi.getElementsByTagName('span')[0];

 aBtn[0].onclick = function () {
  var num = Number(oStrong.innerHTML);
  var price = parseFloat(oEm.innerHTML);
  var numbers = Number(totalNumber.innerHTML);
  var prices = parseFloat(totalPrice.innerHTML);
  num--;
  if (num === 0) {
  // 如果该商品数量为0，,那么就得把它的价格从价格表中清除 
  var index = maxPrice.indexOf(price);
  if (index > -1) maxPrice.splice(index, 1);
  } else if (num < 0) {
  num = 0; 
  return;
  }
  numbers--;
  oStrong.innerHTML = num;
  oSpan.innerHTML = num * price + '元';
  totalNumber.innerHTML = numbers;
  totalPrice.innerHTML = prices - (num + 1) * price;
  mostExpensive.innerHTML = maxPrice[0];

 }
 aBtn[1].onclick = function () {

  var num = Number(oStrong.innerHTML);
  var price = parseFloat(oEm.innerHTML);
  var numbers = Number(totalNumber.innerHTML);
  var prices = parseFloat(totalPrice.innerHTML);

  num++;
  numbers++;
  if (maxPrice.indexOf(price) < 0) {
  maxPrice.push(price)
  maxPrice.sort(function (a,b) {return b - a});
  }
  oStrong.innerHTML = num;
  oSpan.innerHTML = num * price + '元';
  totalNumber.innerHTML = numbers;
  totalPrice.innerHTML = prices + num * price;
  mostExpensive.innerHTML = maxPrice[0];
 }
 }
 function $(id) {return document.getElementById(id);}
}
</script>
</head>

<body>
<ul id="list">
 <li>
 <input type="button" value="-" />
 <strong>0</strong>
 <input type="button" value="+" />
 单价：<em>12.5元</em>
 小计：<span class="highlight">0元</span>
 </li>
 <li>
 <input type="button" value="-" />
 <strong>0</strong>
 <input type="button" value="+" />
 单价：<em>10.5元</em>
 小计：<span class="highlight">0元</span>
 </li>
 <li>
 <input type="button" value="-" />
 <strong>0</strong>
 <input type="button" value="+" />
 单价：<em>8.5元</em>
 小计：<span class="highlight">0元</span>
 </li>
 <li>
 <input type="button" value="-" />
 <strong>0</strong>
 <input type="button" value="+" />
 单价：<em>8元</em>
 小计：<span class="highlight">0元</span>
 </li>
 <li>
 <input type="button" value="-" />
 <strong>0</strong>
 <input type="button" value="+" />
 单价：<em>14.5元</em>
 小计：<span class="highlight">0元</span>
 </li>
</ul>

<p>
商品合计共：<span class="highlight" id="totalNum">0</span>件，
共花费了：<span class="highlight" id="totalPrice">0</span>元<br />
其中最贵的商品单是：<span class="highlight" id="mostExpensive">0</span>元
</p>
</body>
</html>