Explain what a “Singleton” is (in Computer Science terms)

A singleton is a class that allows only a single instance of itself to be created and gives access to that created instance. It contains static variables that can accommodate unique and private instances of itself. … The singleton pattern is used in programming languages such as Java.

Explain how the Singleton pattern can be used with Node modules, specifically with classes

Use the Singleton pattern when a class in your program should have just a single instance available to all clients; for example, a single database object shared by different parts of the program. The Singleton pattern disables all other means of creating objects of a class except for the special creation method.

If you were tasked with building a middleware system like Express uses, what approach might you take to construct/operate it?

1. Execute any code.
2. Make changes to the request and the response objects.
3. End the request-response cycle.
4. Call the next middleware in the stack.

Term	Definition
Router Middleware	The term is composed of 2 words router and middleware. Middleware. It is a piece of code that comes in the middle of request and response . It kind of hijacks your request so that you can do anything that you want with your request or response eg: Modify the data or call the next middleware.
Dynamic Module Loading	Dynamic loading is a mechanism by which a computer program can, at run time, load a library (or other binary) into memory, retrieve the addresses of functions and variables contained in the library, execute those functions or access those variables, and unload the library from memory.
Singleton Pattern	In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one “single” instance. This is useful when exactly one object is needed to coordinate actions across the system. The term comes from the mathematical concept of a singleton.
CRUD -> REST Method Matches	RUD stands for Create, Read, Update, and Delete, which are four primitive database operations. At first glance, these operations map well to the HTTP verbs most frequently used in REST: Create (SQL INSERT) : POST - Used to support the creation of a child resource, but can also modify the underlying state of a system.
Mock Testing	Mock testing is an approach to unit testing that lets you make assertions about how the code under test is interacting with other system modules. In mock testing, the dependencies are replaced with objects that simulate the behaviour of the real ones. … Such a service can be replaced with a mock object.