Build an NPM Module


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

  • Be equipped to break out chunks of code into seperate node modules
  • Push a node module up to NPM


Read this Gold Standard Level blog post by Joanne Daudier

Left Pad Debacle

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

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 npm install npm install -g and npm install --save-dev
    • Why might it be very important to use the --save 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?

An Example

Check out the implementation above. The README contains a ‘more or less’ summary of the steps taken to convert a piece of my Vending Machine Challenge logic into an npm module.


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

You Do

Your challenge, if you choose to accept it, is to take a VERY small amount of logic out of your own repo and break it into an npm module. Go for the smallest possible thing. One helper function is ideal.

Check out a branch on your original repo

  git checkout -b 'npm-refactor'

Pick a very small helper function to break out

In my case, my vending machine challenge code has a prototype function that allows me to load a machine dynamically. I am able to give the function an array of objects

var items = [ {item: 'apple', cost: 2}, 
              { item: 'banana', cost: 1.25},
              { item: 'pear', cost: 2},
              { item: 'strawberry', cost: 1.75},
              { item: 'pineapple', cost: 2.5},
              { item: 'orange', cost: 1},
              { item: 'lime', cost: .5},
              { item: 'lemon', cost: 2},
              { item: 'guava', cost: 2},
              { item: 'mango', cost: 2},
              { item: 'lichee', cost: 2} ];

The function will take the width, number of rows, and depth of each row to assign a button value to each item. The functionality is kind of cool, so it might be something someone else might want to use?

Create an npm module to wrap some functionality in your app

Reference the blog post that you read earlier. Reference the Example Repo. Use the additional resources linked at the bottom of this tutorial. Isolate a very small piece of logic and move it out.

Replace the original code in your original app with the NPM module

Make sure you’re on a branch!!!

Try ‘linking’ to your local version (the example repo has a summary of linking)

Publish your module to NPM

Woo! Time to be famous!

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.