Prevent spotlight from indexing folders with a certain name
There is no known method to exclude from Spotlight a file or a folder based on a pattern (ex.: its name).
However it's possible to exclude a folder from Spotlight by adding to it an empty file .metadata_never_index.
You can use this method to ignore all node_moduleand bower_modules folders:
find /path/to/projects -type d  -path '*node_modules/*' -prune -o -type d -name 'node_modules' -exec touch '{}/.metadata_never_index' \;


Edit:
It look like the method .metadata_never_index is ignored by Spotlight since Mojave.

Edit 2:
As @JohnLee pointed it out, the extended attribute com.apple.metadata:com_apple_backup_excludeItem is not related / doesn't have any impact on Spotlight.
However *.noindex and symlink aren't indexed by mds (the backend of Spotlight). You can use it as band-aid:
# Rename all node_modules to node_modules.noindex and create a symlink node_modules -&gt; node_modules.noindex
find /path/to/projects -type d \( -path '*node_modules/*' -o -path '*node_module.noindex/*' \) -prune -o -type d -name 'node_modules' -exec mv '{}' '{}.noindex' \; -exec ls -s '{}.noindex' '{}' \;

Note: if you use npm-ci, the node_modules is &quot;automatically removed before npm ci begins its install&quot;.