If you're using babel to compile your code, and you decide to compile your dependencies as well, you're going to have a rough time if that package didn't add .babelrc to .npmignore. This is because babel will try to respect that package's presets/plugins configuration, however the code has likely been long since compiled, and the plugins are probably devDependencies, so babel will freak out.
TL;DR Add .babelrc to .npmignore
If you're using babel to compile your code, and you decide to compile your dependencies as well, you're going to have a rough time if that package didn't add .babelrc to .npmignore. This is because babel will try to respect that package's presets/plugins configuration, however the code has likely been long since compiled, and the plugins are probably
devDependencies, so babel will freak out.