Getting data from database and use it to complete

I have the following files:

Main plugin file:

<?php

    /*
    Plugin Name: FixFormData
    Description: If you want to autocomplete a form with existing data, this plugin is for you.
    Version: 1.1
    Author: Stijn Aerts
    Author URI: http://stijnaerts.be
    License: GPL2
    */

    require( plugin_dir_path( __FILE__ ) . 'menu.php');
    require_once( plugin_dir_path( __FILE__ ) . 'getuser.php');


    add_action( 'wp_enqueue_scripts', 'ffd_load_scripts' );

    function ffd_load_scripts()
    {
        wp_register_script('ffd_js_script', WP_PLUGIN_URL.'/FixFormData/js/ffd_js_script.js', array('jquery'));
        wp_localize_script('ffd_js_script', 'myAjax', array(
            'ajaxurl' => admin_url('admin-ajax.php')
            )
        );

        wp_enqueue_script('jquery');
        wp_enqueue_script('ffd_js_script', plugin_dir_url(__FILE__) . 'js/ffd_js_script.js');
    }

getuser.php:

<?php
 function getuser($str)
{
    global $wpdb;

    $myoption =  get_option( 'fixformdata_options' );
    $myoptionValue = maybe_unserialize( $myoption );    

    $result2 = $wpdb->get_row
    (
        $wpdb->prepare
        (
            "SELECT * FROM {$myoptionValue[tablename]} WHERE personeelsNummer = %d", $str
        )
    );

    if($result2) 
    {
        echo  json_encode( $result2 );
    }
}
?>

ffd_js_script.js:

jQuery(document).ready(function($){
    jQuery('#input_1_2').change(function()
    {
        jQuery.ajax({
            type : 'post',
            dataType : 'json',
            url : myAjax.ajaxurl,
            data : {action: 'getuser', this.value},
            succes: function(response){
                var parsed = JSON.parse(response);
                var arr = [];
                for(var x in parsed){ arr.push(parsed[x]);}
                jQuery('#input_1_3').val(arr[1]);
                jQuery('#input_1_4').val(arr[2]);
            }
        })
    });
});

How do I properly implement this? First time I'm making a plugin and I have read much about it and saw alot of examples, but I'm failing to implement this correctly.

EDIT:

IF I replace the sql statement with the following:

"SELECT * FROM {$myoptionValue[tablename]} WHERE personeelsNummer = %s", 1

I get my results in the console due to following code:

echo  json_encode( $result2 );

So following code is not executing properly:

succes: function(response){
                var parsed = JSON.parse(response);
                var arr = [];
                for(var x in parsed){ arr.push(parsed[x]);}
                jQuery('#input_1_3').val(arr[1]);
                jQuery('#input_1_4').val(arr[2]);
            }

ok, you're getting there. 1st When you localize the script add a nonce for better security:

wp_register_script('ffd_js_script', WP_PLUGIN_URL.'/FixFormData/js/ffd_js_script.js', array('jquery'));
wp_localize_script('ffd_js_script', 'myAjax', array(
    'ajaxurl' => admin_url('admin-ajax.php'),
    'nonce'   => wp_create_nonce( 'ajax-nonce' )
    )
);

Then, you need to place getuser.php somewhere where the plugin can see it, so be sure to include it or place it in the main file of the plugin

function getuser($str)
{
    global $wpdb;

    //verify the nonce
    if ( ! wp_verify_nonce( $_REQUEST['_nonce'], 'ajax-nonce' ) )
        die ( 'Non autorizzato!');

    $myoption =  get_option( 'fixformdata_options' );
    $myoptionValue = maybe_unserialize( $myoption );    

    $result2 = $wpdb->get_row
    (
    $wpdb->prepare
    (
        "SELECT * FROM {$myoptionValue[tablename]} WHERE personeelsNummer = %d", $str
    )
    );

    if($result2) 
    {
    echo  json_encode( $result2 );
    }

    die();
}

Than, to make the funciont getuser callable from ajax you need to do the proper hooking:

//ajax hooks
add_action( 'wp_ajax_nopriv_getuser', 'getuser' );
add_action( 'wp_ajax_getuser', 'getuser' );

In the js, you need to pass the nonce as well:

$.post(myAjax.ajaxurl,
     {
        action : 'getuser',
        _nonce : myAjax.nonce, 
        value : $(this).value
     },
     function( response ) { ... });

the rest of the js seems good, forgive me for some typos, I wrote it right here so it's not tested.