JavaScript---通过正则表达式验证表单输入

<script type="text/javascript">
    function submitOn(){
        var f = document.getElementById("userfrm");
        var isValiUserName = false, isValiPassword = false;
        var userNameStr = f.username.value;
        var passwordStr = f.pass.value;
        var rpasswordStr = f.rpass.value;
        if(userNameStr!="" && userNameStr!=undefined){
            //正则表达式验证只能包括字母、数字和下划线字符
            var re = new RegExp(/^[a-zA-Z0-9_]+$/,"ig");
            //正则表达式验证包括字母、数字或下划线，且长度大于等于5，小于等于10
            var re = new RegExp("[a-zA-Z0-9_]{5,10}","ig");
            isValiUserName = re.test(userNameStr); //得到用户名true/false的校验结果
        }
        //校验密码
        if(passwordStr!="" && passwordStr.length>=6 && passwordStr === rpasswordStr){
            isValiPassword = true;
        }
        if(isValiUserName==true && isValiPassword==true)
            return true;
        return false;
    }
</script>

<form id="userfrm" name="userfrm" method="post" action="#">
    登&nbsp;&nbsp;录&nbsp;&nbsp;名：<input name="username" type="text"/><br/>
    密&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;码：<input name="pass" type="password"/><br/>
    重复密码：<input name="rpass" type="password"/><br>
    <input type="button" value="提交" onClick="submitOn()"/>
</form>