为什么点按钮的时候出错呢？ - 编程论坛

程序代码：

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
        <title>Untitled Document</title>
    </head>
    <script>
        function ff(){
            var oDiv = document.getElementById("div1");
            oDiv.style.removeProperty("background-color");

        }
    </script>
    <body>
        <div id="div1" style="background-color:red;height:50px;width:50px" onmouseover="this.style.backgroundColor='blue'">
        </div>
        <input type="button" value="use Methods" onclick="ff();"/>
        </html>