checkForModuleDuplicates

Throw an error when require() may have more than one instance of a module in it's cache due to the module being required with inconsitent module name casing.

Usage

npm install --save checkForModuleDuplicates

Check for duplicates (syncchronously):

require('checkForModuleDuplicates')();

Alternatively, you can check periodically:

require('checkForModuleDuplicates').autocheck();

Explanation

If node is running on a filesystem that's case-insensitive (e.g. MacOSX), require() is case-insensitive. At least, in how it resolves to file paths. So require('foo') and require('FOO') will both resolve to the same 'Foo.js' file. However require()'s module caching is case-sensitive, meaning the module instances you get back in that case are different!

(To make matters worse, require() is case-sensitive for built-in modules. require('http') works, but require('Http') throws, thus reinforcing the naive assumption that nodes insures modules are created as singletons.)

This is the intended behavior, by the way. Unfortunately, it can lead to some really nasty bugs. Nasty, because it won't be at all obvious what the underlying cause of the problem is.

For example, I created this module because I wasted 3 hours tracking down a bug where Sequelize was failing to generate UUIDs. The cause? The Sequelize.UUIDV4 constant I was passing in to Sequelize came from a different instance of the Sequelize module and, thus, wasn't actually recognized as Sequelize.UUIDV4. The fix was to change require('Sequelize') to require('sequelize'). Everything else worked, however... there was no indication given that I had inadvertently created a completely different instance of the module.

So... yeah... fuck that. Never again.