This weekend, I came across an interesting article regarding building a static Bitbucket add-on comprising just HTML, CSS and JS. Generally, add-ons for Atlassian products are built using the connect framework which is based on REST APIs and web hooks. However, it’s also possible to build some add-ons that do not have any server component.
From the README file, it looks like the author hosted the example code on firebase. However, another way to host such add-ons is on Github. Github has had static file hosting support for some time. I used this approach for hosting my version of this example. The biggest convenience is that there is no separate deployment step required. Just pushing the code to Github updates the add-on!