In idiomatic Node, the module is the fundamental unit of logic. Any typical application or system consists of generic code and application code. As a best practice, generic shareable code should be held in discrete modules, which can be composed together at the application level with minimal amounts of domain-specific logic.

In this chapter, we'll learn how Node's module system works, how to create modules for various scenarios, and how we can reuse and share our code.

Let's begin our exploration by setting up a typical file and directory structure for a Node module. At the same time, we'll be learning how to automatically generate a package.json file (we refer to this throughout the book as initializing a folder as a package). We'll also configure npm (Node's package managing tool) with some defaults, which can then be used as part of the package generation process.

In this recipe, we'll create the initial scaffolding for a full Node module.

If Node is on our system, then so is the npm executable...

The Node.js module system, along with its vast ecosystem enables a high degree of composability. A lot of modules are small and do one thing well, and this allows us to composite our own modules on top of other modules.

In this recipe, we will install a dependency.

For this recipe, all we need is Command Prompt open in the hsl-to-hex folder from the Scaffolding a module recipe.

Our hsl-to-hex module can be implemented in two steps:

1. Convert the hue degrees, saturation percentage, and luminosity percentage to corresponding...

Now, it's time to engage in actual implementation details.

In this recipe, we will write some code for our hsl-to-hex module.

Let's ensure that we have a folder called hsl-to-hex, with a package.json file in it. The package.json file should contain hsl-to-rgb-for-reals as a dependency. If there isn't a node_modules folder, we need to ensure that we run npm install from the command line with the working directory set to the hsl-to-hex directory.

To get started, let's create a file called index.js in the hsl-to-hex folder, then open it in our favorite text editor.

In this recipe, we'll prepare our module to be published; then, we'll publish it as a scoped package.

We will publish our hsl-to-hex module that we've been working on in the preceding recipes. We'll also want the (original) tests we wrote in the Adding tests portion of the There's more section of the Writing module code recipe.

If we don't have an npmjs.org account, we'll need to head over to https://www.npmjs.com/signup and get an account. Keep the npm username handy; we will need it.

There can be multiple reasons for using a private repository. From a personal perspective, it can be a useful caching mechanism or test-bed when run locally. From an organizational perspective, it's usually about control.

While open source has been fundamental to advancements in every industry that has been touched by the digital era, there's still a case for in-house only code. In some cases, it may be that code is specific to an organization or reveals internal details that should be trade secrets. In other cases, it may be an archaic though impassable proprietary culture. At any rate, it makes all the more sense to share resources when living in a gated community.

In this recipe, we'll investigate setting up a personal module registry that can be deployed as an internal registry to provide a platform for code reuse across an organization...