You can conditionally echo the code on only few templates or specific pages. Here is an example:
add_action ( 'wp_head', 'my_js_variables' );
function my_js_variables(){
// for specific page templates
$current_template = get_page_template();
// return if there is no page template, or if the page template is other than template-x1.php or template-x2.php
if( !isset($current_template) || ( $current_template != 'template-x1.php' && $current_template != 'template-x2.php' ) ){ return; } ?>
<script type="text/javascript">
var ajaxurl = <?php echo json_encode( admin_url( "admin-ajax.php" ) ); ?>;
var ajaxnonce = <?php echo json_encode( wp_create_nonce( "itr_ajax_nonce" ) ); ?>;
var myarray = <?php echo json_encode( array(
'foo' => 'bar',
'available' => TRUE,
'ship' => array( 1, 2, 3, ),
) ); ?>
</script>
<?php
}