Mongoose JS findOne always returns null
Mongoose pluralizes the name of the model as it considers this good practice for a "collection" of things to be a pluralized name. This means that what you are currently looking for in code it a collection called "users" and not "user" as you might expect.
You can override this default behavior by specifying the specific name for the collection you want in the model definition:
var userModel = mongoose.model('user', userSchema, 'user');The third argument there is the collection name to be used rather than what will be determined based on the model name.