Best practice - i tohle jsou studenti schopni mi odevzdat

controller.php

<?php

class indexController extends Controller {

    public $head = 1;
    var $name = "Vytvoření účtu";

    /**
     * Automatický text pro template - titulek (TITLE)
     */
    public function name() {
        echo ' - ' . $this->name;
    }

    /**
     * Automatický text pro template - text
     */
    public function index() {
        ?><h2>Vytvořte si svůj účet</h2>
        <form name="login" action="index.php?url=createAccount" method="post" onsubmit='return check(this);' accept-charset="utf-8">  
            <ul>  
                <li><input type="text" name="nick" id ="nick" placeholder="login" value="" tabindex="1" onclick ="isFreeNick(this.value)" onkeyup="isFreeNick(this.value)" required><label for="usermail">Nickname</label></li>  
                <li><input type="password" name="pass" id ="pass" placeholder="password" value=""  tabindex="2" required><label for="password">Password</label></li>  
                <li><input type="email" name="mail" id="mail" placeholder="email@email.com" value=""  tabindex="3"onclick ="isFreeMail(this.value)" onkeyup="isFreeMail(this.value)" required><label for="password">Email</label></li>  
                <li><input type="submit" value="Login" tabindex="4"></li>  
            </ul>  
        </form>
        <p>Zde se zobrazí, zda je NICK již použit: <span id="nickTell"></span></p>
        <p>Zde se zobrazí, zda je MAIL již použit: <span id="mailTell"></span></p>
            <?php
        }

        /**
         * Pozměněn pouze pro zobrazení LogIn
         */
        public function aside() {
            $aside = new Aside();
            $aside->makeLogIn();
        }

        /**
         * Hlavička vložená do template - použito pro JS (s AJAX)
         */
        public function header() {
            ?>
        <script>
            document.onload = function() {
                <?php 
                if(isset($_SESSION['nick']))echo "document.getElementById('nick').value = ".$_SESSION['nick'];
                if(isset($_SESSION['email']))echo "document.getElementById('mail').value = ".$_SESSION['email'];
                
                ?>;
            };
            function isFreeNick(str)
            {
                if (str.length == 0)
                {
                    document.getElementById("nickTell").innerHTML = "";
                    return;
                }
                var xmlhttp = new XMLHttpRequest();
                xmlhttp.onreadystatechange = function()
                {
                    if (xmlhttp.readyState == 4 && xmlhttp.status == 200)
                    {
                        if (xmlhttp.responseText === "Není volný!") {
                            document.getElementById("nickTell").style.color = "red";
                        }
                        document.getElementById("nickTell").innerHTML = xmlhttp.responseText;
                    }
                }
                xmlhttp.open("GET", "index.php?url=help/nick/" + str, true);
                xmlhttp.send();
            }
            function isFreeMail(str)
            {
                if (str.length == 0)
                {
                    document.getElementById("mailTell").innerHTML = "";
                    return;
                }
                var xmlhttp = new XMLHttpRequest();
                xmlhttp.onreadystatechange = function()
                {
                    if (xmlhttp.readyState == 4 && xmlhttp.status == 200)
                    {
                        if (xmlhttp.responseText === "Není volný!") {
                            document.getElementById("mailTell").style.color = "red";
                        }
                        document.getElementById("mailTell").innerHTML = xmlhttp.responseText;

                    }
                }
                xmlhttp.open("GET", "index.php?url=help/mail/" + str, true);
                xmlhttp.send();
            }
            function check(send)
            {
                if (document.getElementById("nickTell").innerHTML === "" && send.nick.value !== "" ||
                        document.getElementById("mailTell").innerHTML === "" && send.mail.value !== "" ||
                        document.getElementById("nickTell").innerHTML === "Není volný!" ||
                        document.getElementById("mailTell").innerHTML === "Není volný!") {
                    return false;
                }
            }
        </script>
        <?php
    }

}
?>