A buddy of mine just blundered into this trap/pitfall while including jQuery into a project. Both jQuery and jquery do exist in npm’s registry. While the latter is the one he was looking for, he snapped the former (due to »jQuery« being the official notation). This caused a lot of (reasonable) confusion.
In its earliest days, npm allowed packages to include any URL-safe character in their names, including upper and lower case. Since 2013, it’s not possible to create new packages with upper-case letters in the name anymore, but packages with upper-case letters in their names are still in the registry and still in use (due to backward compatibility reasons).
While npm’s main motivation was to restrain typosquatting (i.e. providing a package for malicious purposes with a very similar name), these packages also cause problems if you’re installing them on case-insensitive file systems (such as the file systems on most macOS computers if not configured differently). For example, it’s not possible to install both the jquery and jQuery package at the same time. Both will be listed within package.json, but only one version can exist on the file system (i.e. the package installed last).
