绑定Dom对象属性时候出错？
代码如下：
<head> <title>Exercise</title></head><body> <div> <h2>数据校验表单</h2> <form method="post" name="register" action="#"> 用户名：<input type="text" name="user" /><br /> 密 码：<input type="password" name="pass" /><br /> 电 邮：<input type="text" name="email" /><br /> <input type="submit" value="提交" /><br /> </form> </div> <script type="text/javascript"> String.prototype.trim = function() { return this.replace(/^\s*/, "").replace(/\s*$/, ""); } var check = function() { var form = document.forms[0]; var errStr = ""; if (form.user.value == null || form.user.value.trim() == "") { errStr += "\n用户名不能为空!"; form.user.focus(); } if (form.pass.value == null || form.pass.value.trim() == "") { errStr += "\n密码不能为空!"; form.pass.focus(); } if (form.email.value == null || form.email.value.trim() == "") { errStr += "\n电子邮件不能为空!"; form.email.focus(); } if (!/^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/.test(form.email.value.trim())) { errStr += "\n电子邮件的格式不正确!"; form.email.focus(); } if (errStr != "") { alert(errStr); return false; } } document.form[0].onsubmit = check; </script></body>