It would be a great (and I think simple) idea to add an "Output" folder in the settings, PER PROJECT, that allows to copy files to it prior to running the preview server. This simple addition would allow me to set a path to a "project/public" or "project/www" folder, which would be a sub-folder of my backend project. That way I can build and work on the back-end separately, and upon running the preview in BSS, it can load the files from that folder.
Example: Let's say I have this structure:
MyProject
MyProject/www/javascript
MyProject/www/css
MyProject/server
MyProject/client
I could compile my project, which would output the .js files from client (I use TypeScript) to the www/javascript folder. Then I would hit the "Preview" button in the front-end designer, and it would update anything changed in the folder, and the built-in web server could then load the files from there.
There's an alternative idea:
You already allow linking to external files using a URL. Why not support the "file:///C:/dir/somefile.ext" format for files, then import anything that changed prior to preview? (example: file://C:/SomeDir/etc/MyProject/www/javascript/app.js) I tried and it does not work, because BSS creates a <script> tag and just dumps the URL in there (which does not work for security reasons, obviously). Instead, DETECT the file:// URL and IMPORT those files prior to preview - especially since direct file references never work well anyhow due to most browser security. Of course it would require translating the <script> tag src path to reference the imported file instead when preview is clicked.