I found this script online and have been experimenting with it. However, I encountered the following error:

SyntaxError: JSON.parse: unexpected character

[Break On This Error]

var res = JSON.parse(result);

The problem lies in the file below as I am unfamiliar with JSON operations.

Error-causing file: register.js

$(document).ready(function () {
//button register click
$("#btn-register").click(function () {
    if(register.validateRegistration() === true) {
        //validation passed
        var regMail     = $("#reg-email").val(),
            regUser     = $("#reg-username").val(),
            regPass     = $("#reg-password").val(),
            regPassConf = $("#reg-repeat-password").val(),
            regBotSsum  = $("#reg-bot-sum").val();

        //create data that will be sent to server
        var data = { 
            userData: {
                email           : regMail,
                username        : regUser,
                password        : regPass,
                confirm_password: regPassConf,
                bot_sum         : regBotSsum
            },
            fieldId: {
                email           : 'reg-email',
                username        : 'reg-username',
                password        : 'reg-password',
                confirm_password: 'reg-repeat-password',
                bot_sum         : 'reg-bot-sum'
            }
        };

        //send data to server
        register.registerUser(data);
    }                        
});
});



/** REGISTER NAMESPACE
 ======================================== */

var register = {};


/**
 * Registers new user.
 * @param {Object} data Register form data.
 */
register.registerUser = function (data) {
//get register button
var btn = $("#btn-register");

//put button to loadin state
asengine.loadingButton(btn, "Creating acount...");

//hash passwords before send them through network
data.userData.password = CryptoJS.SHA512(data.userData.password).toString();
data.userData.confirm_password = CryptoJS.SHA512(data.userData.confirm_password).toString();

//send data to server
$.ajax({
    url: "ASEngine/ASAjax.php",
    type: "POST",
    data: {
        action  : "registerUser",
        user    : data
    },
    success: function (result) {
        //return button to normal state
        asengine.removeLoadingButton(btn);

        //parse result to JSON
        var res = JSON.parse(result);

        if(res.status === "error") {
            //error

            //display all errors
            for(var i=0; i<res.errors.length; i++) {
                var error = res.errors[i];
                asengine.displayErrorMessage($("#"+error.id), error.msg);
            }
        }
        else {
            //display success message
            asengine.displaySuccessMessage($(".register-form fieldset"), res.msg);
        }
    }
});
};



register.validateRegistration = function () {
var valid = true;

//remove previous error messages
asengine.removeErrorMessages();


//check if all fields are filled
$(".register-form").find("input").each(function () {
    var el = $(this);

    if($.trim(el.val()) === "") {
        asengine.displayErrorMessage(el);
        valid = false;
    }
});

//get email, password and confirm password for further validation
var regMail     = $("#reg-email"),
    regPass     = $("#reg-password"),
    regPassConf = $("#reg-repeat-password");

//check if email is valid
if(!asengine.validateEmail(regMail.val()) && regMail.val() != "") {
    valid = false;
    asengine.displayErrorMessage(regMail,"Please insert valid email.");
}

//check if password and confirm password fields are equal
if(regPass.val() !== regPassConf.val() && regPass.val() != "" && regPassConf.val() != "") {
    valid = false;
    asengine.displayErrorMessage(regPassConf, "Passwords don't match.");
}

return valid;
};

ASRegister.php

<?php

/**
 * User registration class.
 *
 */
class ASRegister extends ASDatabase{

//local ASEmail object
private $mailer;

function __construct() {

    //connect to database
    parent::__construct(DB_TYPE, DB_HOST, DB_NAME, DB_USER, DB_PASS);

    //create new object of ASEmail class
    $this->mailer = new ASEmail();
}

/**
 * Register user.
 * @param array $data User details provided during the registration process.
 */
public function register($data) {
    $user = $data['userData'];

    //validate provided data
    $errors = $this->_validateUser($data);

    if(count($errors) == 0) {
        //no validation errors

        //generate email confirmation key
        $key = $this->_generateKey();

        //insert new user to database
        $this->insert('as_users', array(
            "email"     => $user['email'],
            "path"      => strtolower(str_replace(' ','',$name)),
            "username"  => strip_tags($user['username']),
            "password"  => $this->hashPassword($user['password']),
            "confirmation_key"  => $key,
            "register_date"     => date("Y-m-d")     
        ));

        //send confirmation email
        $this->mailer->confirmationEmail($user['email'], $key);

        //prepare and output success message
        $result = array(
            "status" => "success",
            "msg"    => SUCCESS_REGISTRATION
        );

        echo json_encode($result);

    }
    else {
        //there are validation errors

        //prepare result
        $result = array(
            "status" => "error",
            "errors" => $errors
        );

        //output result
        echo json_encode ($result);
    }
}

/**
 * Check if user with given username exist.
 * @param string $username Given username.
 * @return boolean TRUE if user already exist, false otherwise.
 */
public function doesUserExist($username) {
    if(!$this->_isUsernameAvailable($username))
        return true;
    return false;
}


/**
 * Check if email already exist in database.
 * @param string $email Email to check.
 * @return boolean TRUE if email exist, FALSE otherwise
 */
public function doesEmailExist($email) {
    return !$this->_isEmailAvailable($email);
}


/**
 * Send forgot password email.
 * @param string $userEmail Provided email.
 */
public function forgotPassword($userEmail) {
    //we only have one field to validate here
    //so we don't need id's from other fields
    if($userEmail == "")
        $errors[] = ERROR_EMAIL_REQUIRED;
    if(!$this->_validateEmail($userEmail))
        $errors[] = ERROR_EMAIL_WRONG_FORMAT;

    if($this->doesEmailExist($userEmail) == false)
        $errors[] = ERROR_EMAIL_NOT_EXIST;

    if(count($errors) == 0) {
        //no validation errors

        //generate password reset key
        $key = $this->_generateKey();

        //write key to db
        $this->update(
                    'as_users', 
                     array("password_reset_key" => $key), 
                     "`email` = :email",
                     array("email" => $userEmail)
                );

        //send email
        $this->mailer->passwordResetEmail($userEmail, $key);
    }
    else
        echo json_encode ($errors); //output json encoded errors
}


/**
 * Reset user's password if password reset request has been made.
 * @param string $newPass New password.
 * @param string $passwordResetKey Password reset key sent to user
 * in password reset email.
 */
public function resetPassword($newPass, $passwordResetKey) {
    $pass = $this->hashPassword($newPass);
    $this->update(
                'as_users', 
                array("password" => $pass), 
                "`password_reset_key` = :prk ",
                array("prk" => $passwordResetKey)
            );
}


/**
 * Hash given password.
 * @param string $password Unhashed password.
 * @return string Hashed password.
 */
 public function hashPassword($password) {
    //this salt will be used in both algorithms
    //for bcrypt it is required to look like this,
    //for sha512 it is not required but it can be used 
    $salt = "$2a$" . PASSWORD_BCRYPT_COST . "$" . PASSWORD_SALT;

    if(PASSWORD_ENCRYPTION == "bcrypt") {
        $newPassword = crypt($password, $salt);
    }
    else {
        $newPassword = $password;
        for($i=0; $i<PASSWORD_SHA512_ITERATIONS; $i++)
            $newPassword = hash('sha512',$salt.$newPassword.$salt);
    }

    return $newPassword;
 }


/**
 * Generate two random numbers and store them into $_SESSION variable.
 * Numbers are used during the registration to prevent bots to register.
 */
 public function botProtection() {
    ASSession::set("bot_first_number", rand(1,9));
    ASSession::set("bot_second_number", rand(1,9));
}


 /* PRIVATE AREA
 =================================================*/


/**
 * Validate user provided fields.
 * @param array $data User provided fieds and id's of those fields that will 
 * be used for displaying error messages on client side.
 * @return array Array with errors if there are some, empty array otherwise.
 */
private function _validateUser($data) {
    $id     = $data['fieldId'];
    $user   = $data['userData'];
    $errors = array();

    //check if email is not empty
    if($user['email'] == "")
        $errors[] = array( 
            "id"    => $id['email'],
            "msg"   => ERROR_EMAIL_REQUIRED 
        );

    //check if username is not empty
    if($user['username'] == "")
        $errors[] = array( 
            "id"    => $id['username'],
            "msg"   => ERROR_USERNAME_REQUIRED
        );

    //check if password is not empty
    if($user['password'] == "")
        $errors[] = array( 
            "id"    => $id['password'],
            "msg"   => ERROR_PASSWORD_REQUIRED
        );

    //check if password and confirm password are the same
    if($user['password'] != $user['confirm_password'])
        $errors[] = array( 
            "id"    => $id['confirm_password'],
            "msg"   => ERROR_PASSWORDS_DONT_MATCH
        );

    //check if email format is correct
    if(!$this->_validateEmail($user['email']))
        $errors[] = array( 
            "id"    => $id['email'],
            "msg"   => ERROR_EMAIL_WRONG_FORMAT
        );

    //check if email is available
    if($this->_isEmailAvailable($user['email']) == false)
        $errors[] = array( 
            "id"    => $id['email'],
            "msg"   => ERROR_EMAIL_TAKEN
        );

    //check if username is available
    if($this->_isUsernameAvailable($user['username']) == false )
        $errors[] = array( 
            "id"    => $id['username'],
            "msg"   => ERROR_USERNAME_TAKEN
        );

    //bot protection
    $sum = ASSession::get("bot_first_number") + ASSession::get("bot_second_number");
    if($sum != intval($user['bot_sum']))
        $errors[] = array( 
            "id"    => $id['bot_sum'],
            "msg"   =>ERROR_WRONG_SUM
        );


    return $errors;
}


/**
 * Check if email is available.
 * @param string $email Email to be checked.
 * @return boolean TRUE if email is available, FALSE otherwise
 */
private function _isEmailAvailable($email) {
    $query = "SELECT * FROM `as_users` WHERE `email` = :e ";
    $result = $this->select($query, array( "e" => $email ));
    if(count($result) == 0)
        return true;
    else
        return false;
}


/**
 * Check if username is available.
 * @param string $un Username to check.
 * @return boolean TRUE if username is available, FALSE otherwise.
 */
private function _isUsernameAvailable($un) {
    $query = "SELECT * FROM `as_users` WHERE `username` = :u ";
    $result = $this->select($query, array( "u" => $un ));
    if(count($result) == 0)
        return true;
    else
        return false;
}


/**
 * Check if email has valid format.
 * @param string $email Email to be checked.
 * @return boolean TRUE if email has valid format, FALSE otherwise.
 */
private function _validateEmail($email) {
    return preg_match("/^[_a-z0-9-]+(\.[_a-z0-9+-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,})$/i", $email);
}


/**
 * Generate key used for confirmation and password reset.
 * @return string Generated key.
 */
private function _generateKey() {
    return md5(time() . LOGIN_SALT . time());
}


}

?>