How to make Dropbox ignore node_modules folder with symbolic links (aliases)

NOTE: The Initial Post on this thread IS the Solution. While the technique specifically targets the node_modules folder in Javascript / TypeScript projects, it can also be applied to any "folders" that need to be ignored (see bottom of this post for a drag-n-drop technique).

HOW IT WORKS

Because Dropbox does not synchronize folders referened by symlinks (aliases), you can move those folders into a NON-DROPBOX path (outside of dropbox), then create a symlink (alias) in the original Dropbox location.

RESULT

The ignored folder in Dropbox looks and behaves as normal folder, but in reality the data lives in a non-synchronized location on the storage device.

HOW TO IGNORE ANY FOLDER (THE DRAG-N-DROP WAY)

1. Move the folder to ignore "Outside of Dropbox" into another location (e.g. ~/Documents)
2. In Finder (Mac OS), Command+Option Drag the folder back into Dropbox to create an alias. The cursor should turn into a little curved arrow while dragging if you have the right keys pressed. Once dropped, an alias will be created in the original Dropbox location pointing to the moved folder.

NOTE: Using symlinks/aliases on Windows and Linux should behave the same way, but I have not verified it. Also, I've updated the original post to state that the tiny symlink (alias) file itself "IS" copied to all systems, but not the content of the folder.

..sebastian