How to Stringify one JSON object while keeping the other an integer

On the PHP side of things, I have an integer and I have a string of HTML:

function get_the_goods() {

$versionid = '7';

$htmlstuff = '';
$htmlstuff .= '<div id="kittens">STUFF AND STUFF</div><img src="https://example.com">';
$htmlstuff .= '<p>KITTENS THE SEQUEL.</p>';

echo "{'versionid':'" . $versionid . "','htmlstuff':'" . $htmlstuff . "'}";

wp_die();

}

$versionid is just an integer and $htmlstuff is a reasonable string of HTML. I escaped the double quotes trying to resolve this.

When I parse this as such on the JQuery/JS side, I get an unexpected token error. Previously, I was only sending the string of HTML by itself without the JSON array and all was fine.

//THIS IS THE RELEVANT JQUERY/AJAX PART:

                   success : function(data){

                           if(data && data !="") {

                             var json = JSON.parse(data);

                              var htmlstuff = json.htmlstuff;

                                var previousversion = json.versionid;

                                 console.log(versionid);
                                 jQuery('#kittens).html(htmlstuff);


                       }

                       }

Answer

My solution to this problem was simple. Instead of attempting to echo the JSON myself, I put it into a PHP array and used JSON_ENCODE to prep it for jQuery and this ended up working fine.