jQuery ajax load not a function

Here's a screenshot of the jquery downloads from the jquery download page (https://jquery.com/download/)
It is easy NOT to notice this line.
Since many people are using jquery ajax, maybe they should rename the file as jquery-slim-no-ajax.js

First of all, make sure you don't include jquery library after your js code! Especially be careful if you use bootstrap!

I had the problem - I didn't see the part of bootstrap code in the footer.php, which had another jquery library - which caused the problem.

https://code.jquery.com/jquery-3.2.1.slim.min.js is the slim edition of jquery, which does not include ajax. slim is the default version included in an Express server. Use the full version of jquery at https://code.jquery.com/jquery-3.2.1.min.js