MongoDB via Mongoose JS - What is findByID?

As opposed to find() which can return 1 or more documents, findById() can only return 0 or 1 document. Document(s) can be thought of as record(s).

If the schema of id is not of type ObjectId you cannot operate with function : findbyId()

findById is a convenience method on the model that's provided by Mongoose to find a document by its _id. The documentation for it can be found here.

Example:

// Search by ObjectId
var id = "56e6dd2eb4494ed008d595bd";
UserModel.findById(id, function (err, user) { ... } );

Functionally, it's the same as calling:

UserModel.findOne({_id: id}, function (err, user) { ... });

Note that Mongoose will cast the provided id value to the type of _id as defined in the schema (defaulting to ObjectId).