Build an NPM Module

source: Stolen and altered from Meeka’s mod 4 lesson


By the end of this lesson, you will know/be able to:

  • Be equipped to break out chunks of code into seperate node modules
  • Better understand the pros and cons of node modules
  • Push a node module up to NPM


Read this Gold Standard Level blog post by Joanne Daudier

Note: don’t code along, that will come later

Note: don’t worry about things you don’t understand or recognize (i.e. mentions of Travis CI or Coveralls)

Note: as you read, prepare answers to the following discussion points

Reading Discussion Points

  • What is SemVer

  • What is the difference between npm install --save-prod npm install npm install -g and npm install --save-dev
    • Why might it be very important to use the --save-prod and --save-dev flags appropriately for an NPM package?
  • Having read this blog, what steps might be missing for you to create your own node module and deploy it?

  • What npm packages do you depend on? Have you ever looked at their source code?

  • How might the fact that you don’t control the version of the package that your users use affect your workflow?


Relevant NPM commands


If you have a local directory containing an npm package, you can link this package locally.

cd module-name
npm link

When you want to use a local linked package, you can do so with link

 mkdir newapp/
 cd newapp/
 npm link module-name

To unlink a package from an application:

cd newapp/
npm unlink module-name

To unlink a package from your system:

 cd module-name
 npm unlink

addUser or login


 npm adduser
 npm login

publish & unpublish


 cd module-name
 npm publish
 npm unpublish module-name

--access public or --access restricted - flag to set as public



You can specify a scope for an NPM module to prevent naming collisions with other modules



Bump an npm version when you add relevant information or code

  npm version <versions> -m "message"

version: patch, minor, major, prepatch, preminor, premajor, prerelease

  npm version patch -m "Update Documentation"

This will bump your version automatically, and prepare to version.


  git push
  npm publish

Outside Resources / Further Reading

Reading Discussion Point Answers

  • SemVer stands for semantic versioning
  • The --save-dev flag means that the dependency is only used by developers. The --save flag means that this dependency has to be used for the package to work in production. It really matters here. When people include your npm module in their node_modules folder, the dev dependencies won’t come along for the ride. That’s important, because number of lines of code matter for the speed of an application. If you completely omit the --save flag, then your npm module won’t work when other folks pull it down.

Set Up a Basic NPM Module

Create a new directory named after your new fancy node module (USE lowercase ONLY!)

$ mkdir name-of-module

We’ll want to add some files:

  • A to explain how to set up and use our module
  • an index.js file to contain our code (more complex packages may use more than one file)
  • A test folder with a test.js file in it
$ echo "# Name of Node Module" >>
$ mkdir test
$ touch index.js test/test.js

Next we need to describe our package with a package.json file. Because we’re not creating any revolutionary node modules that thousands of developers will use, we should namespace our module to ensure we don’t take up any hot module names (i.e. don’t name it jquery-2)

$ npm init --scope=username

Follow the instructions in your terminal to complete your package.json file. Some things to keep in mind:

  • name: the default will be @username/project-name, you need to change “@username” to be your npm account username
  • Version: think about what you read about Semantic Versioning
  • License: ISC is fine, but what is it?

One more thing before we write the code for our module, we need to bring in mocha for testing and set up our test file:

$ echo "node_modules/" >> .gitignore
$ npm i mocha -D
$ npm i chai -D

Fun facts!

-D is the same as --save-dev
-S is the same as --save

In your test.js file include the following:

const chai = require('chai')
const expect = chai.expect

In your index.js file include the following:

const bubbleSort = (array) => {
  for (let j = 0; j < array.length; j++) {
    for (let i = 0; i < array.length - 1; i++) {
      if (array[i] > array[i + 1]) {
        [ array[i], array[i + 1] ] = [ array[i + 1], array[i] ]
  return array;

module.exports = {


If we were going to publish this, we’d do …

  npm publish --access=public

Log into your npm account and see your published module live on the internets! To bring it into another project, all you have to do is npm install your-module and require it into any file where you need to use it. Voila! That’s it!

Now unpublish your node module so we’re not muddying up npm with a bunch of repetitive modules :).

  npm unpublish --force

But instead, we’re going to do this:

There’s Another Way!

You can actually import modules/packaged code from GitHub repos. It’s as easy as typing:

npm install [GitHub URL] -S

and then requiring a specific module in your js file as you would with any other module.

For this to work, make sure you are still bundling up your code with that module.exports.


In the file you are packaging up into a module:

  1. Use module.exports to export the relevant functionality from your files.
  2. Use require() with the relative filepath to import the significant functionality into the index.js file.
  3. Use module.exports to export the functionality from the index.js file.
  4. In the package.json file, make sure it includes a "name" property set to "@yourusername/your-project-name"
  5. In the package.json file, make sure it includes a "main" property set to the filepath of your "index.js"
  6. Add and commit your changes, push up to GitHub.

In the project you want to use the module in:

  1. Run npm install [THE URL OF THE MODULE'S GITHUB REPO] + the appropriate flag --save-prod or --save-dev
  2. In whatever file you wish to use the module in, import it in import [NAME OF MODULE] from '@yourusername/your-project-name' OR const [NAME OF MODULE] = require('@yourusername/your-project-name') NOTE: if this project will ALSO be turned into a module, use the module.exports/require syntax!
  3. Use your module and bask in the glow of keeping your project lean by importing in functionality!

If you need to update your module:

  1. Update your module!
  2. Update the version number in your package.json
  3. Add, commit, and push your changes to GitHub
  4. In the project where you are using your module: a) Delete the package-lock.json file b) Run npm install [THE URL OF THE MODULE'S GITHUB REPO] + the appropriate flag --save-prod or --save-dev c) Open up the node_modules, find the module, and check that the module has been updated

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