send back undefined in ajax

hi
in this ajax , returns the “undefined” in alert …
it’s my code :

php func :

<?php
	function myfunc(){
		$arr = array(
			'var' => 'hello',
		);
		echo json_encode($arr);
	}
	add_action('wp_ajax_myfunc', 'myfunc');
	add_action('wp_ajax_nopriv_myfunc', 'myfunc');
?>

and jq :

<script type="text/javascript">
	$(function(){
		$.ajax({
			type: 'post',
			url: "<?php echo admin_url("admin-ajax.php"); ?>",
			dataType: 'json',
				data: {
					action : 'myfunc',
				},
				success: function(data) {
					alert(data.var);
				}
		});
	});
</script>

and also i tried ” alert(data); ” but returns the 0