Function echos variable correctly to ajax file but in html doesn't show anything

Question

Php variable $testing correctly echos ajax file, but in html <?php echo $testing;?> doesn't show anything.

Answer 1

Okay as the comments says I missunderstood how ajax works.

So the answer why it doesnt show anything is - php generates page and script and then the ajax script sends data to php file. To get ajax file data output I need to write JS which gonna put it into html - which is another question how to do that.