function checkLog() {

    //用户名
    var VlogName = document.Log.logName.value;
    if (checkspace(VlogName) || VlogName.length < 4 || VlogName.length > 16) {
        alert("请输入正确的用户名！");
        document.Log.logName.focus();
        return;
    }

    //真实姓名
    var VlogPwd = document.Log.logPwd.value;
    if (checkspace(VlogPwd) || VlogPwd.length < 6 || VlogPwd.length > 20) {
        alert("请输入正确的密码!");
        document.Log.logPwd.focus();
        return;
    }
    document.Log.submit();
}

function checkspace(checkstr) {
    var str = '';
    for (i = 0; i < checkstr.length; i++) {
        str = str + ' ';
    }
    return (str == checkstr);
}