编程练习，用JS实现购物车特效教程-慕课网

index.html
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        input { width: 60px; }
        div { margin: 10px 0 }
    </style>
    <script type="text/javascript">
        window.onload = function () {
 
            // 获取元素
            var num1 = document.getElementById('num1');
            var num2 = document.getElementById('num2');
            var ret = document.getElementById('ret');
            var btns = document.getElementsByTagName('button');
            var p = parseInt;
 
            //为按钮添加点击事件，计算结果
 
 
 
 
 
 
        }
    </script>
</head>
<body>
<input id="num1" type="text"/>
<input id="num2" type="text"/>
<div>结果：<span id="ret"></span></div>
<button>+</button>
<button>-</button>
<button>*</button>
<button>/</button>
</body>
</html>
编程练习

任务
