请教大神这段javascript脚本的问题
<head runat="server">
<script type="text/javascript" language="javascript">
function calcu() {
var num1 = document.getElementById('txtNum1');
var num2 = document.getElementById('txtNum2');
var total = parseFloat(num1) * parseFloat(num2);
document.getElementById('result').= total;
}
</script>
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
竞拍价格:<asp:TextBox ID="txtNum1" runat="server" ></asp:TextBox>
<br /> 购买数量:<asp:TextBox ID="txtNum2" runat="server"></asp:TextBox>
<br /> 预计总价:<asp:TextBox ID="result" runat="server"></asp:TextBox>
<br /> <asp:Button ID="btn1" runat="server" Text="计算看看" OnClientClick="calcu()"/>
没有运行结果 是不是哪里写错了