I love ack and its very not opinionated domain ;)
But, trying to use it on a Node project without some tweaks was a nightmare. This is because, among other issues, by default, it crawled the entire node_modules directory looking for your search query.
Adding a ~/.ackrc file (or modifying your existing one) and adding the following will fix this problem:
# Make ack Node friendly :) --ignore-dir=node_modules --type-set=coffee=.coffee --type-set=jade=.jade --type-set=json=.json
These bits tell ack to ignore the node_modules directory, and to ensure it checks in some filetypes it would otherwise ignore.