Closing ajax function file with die() causes error and empty page

Question

Adding die(); to the end of my ajax function file gives me totally blank page and this error in Firebug:

The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must to be declared in the document or in the transfer protocol.

I scaled down to a very basic ajax function file:

<?php
function show_article(){
$q = $_GET['getid'];

echo strval($q);
}

die();
?>

Which still gives the empty page and error. Without die(); at the close, it works as expected but with the extra 0 at the end of the echoed $q value.

I'm not sure what is causing this issue. For extra context, here's what I've got in my functions.php file.

function ajaxscripts() {
wp_enqueue_script( 'productajax', get_template_directory_uri().'/js/productajax.js', false, null, false );  
wp_localize_script( 'productajax', 'myajax', array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) ) );
}
add_action('wp_enqueue_scripts', 'ajaxscripts');

$dirName = dirname(__FILE__);
$baseName = basename(realpath($dirName));
require_once ("$dirName/getarticle.php"); //my ajax function file

add_action( 'wp_ajax_nopriv_show_article', 'show_article' );
add_action( 'wp_ajax_show_article', 'show_article' );

Answer 1

The die should be in your show_article() function. Yours is out, so the whole script is terminated. Your function should be:

function show_article(){
  $q = $_GET['getid'];
  echo strval($q);
  die;
}

or

function show_article(){
  $q = $_GET['getid'];
  exit( strval($q) );
}

Answer 2

Your die() is outside the function show_article().