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13 months with Yarn Yarn solved the annoying problems we faced using npm, but it came with issues of its own:

Yarn has shipped very bad regressions, which made us afraid of upgrading. Yarn often produces yarn.lock files that are invalid when you run add, remove, or update. This results in engineers needing to perform tedious work to remove and add offending packages until Yarn figures out how to untangle itself so that yarn check passes. Frequently when engineers would run yarn after pulling down a project's latest changes, their yarn.lock files would become dirty due to Yarn making optimizations. Resolving this required engineers to make and push commits unrelated to their work. Yarn should perform these optimizations when commands update yarn.lock, not the next time yarn is run. yarn publish is unreliable (broken?) (tracked issues #1, tracked issue #2), which meant that we had to use npm publish to publish packages. It was easy to forget that we needed to use npm in this special case and accidentally publishing with Yarn resulted in published packages being un-installable. Unfortunately, none of these workflow-breaking issues were fixed during the 13 months we used Yarn.

After a couple of especially painful weeks full of 15-minute Yarn untangling sessions, we decided to take a look at moving back to npm.