How to remove .php at the end of the address of each web page of the site?

Question

PHP

I know that it can be removed with the .htaccess file, but I have ajax with the php extension in my js file (example:

const url = "/ajax/ajax.preReg.php?name="+user_name;

)
and if I remove php from there, then everything will break
. Is it possible to somehow modify .htaccess or is there another way?