NPM & Tooling

Learning Goals

  • What is NPM, why do we use it, and what does it do for us?
  • Identify factors in choosing a package
  • See how a package interacts with an application


  • Package Manager - a registry where developers can publish small, reusable pieces of code that they’ve written and would like others to be able to incorporate into their projects
  • Package - small, independent piece of reusable code that often solves a commonplace problem
  • Dependency - a package that your project relies on in order to function properly
  • Configuration File - a file that allows you to define how a particular tool you’re using should interact with your codebase

Tooling for Complex Apps

As developers, we use a lot of tools to facilitate building our applications - from text editors, to browsers, to consoles. It takes a lot of tooling to build even the simplest of applications.

As our apps grow to be more complex, our toolbox is going to grow as well. So far, we’ve added quite a few things to your toolkit without really digging deep into what they do, why we use them, and how they work. So today we’re going to shed some light on them. Specifically, we’ll be talking about NPM.


The NPM Configuration Files: package.json and package-lock.json

NPM stands for Node Package Manager. A package manager is a registry where developers can publish reusable pieces of code that they’ve written (a package), and allow other developers to download it directly into their projects (as a dependency). NPM is not the only package manager - you may see others such as Yarn or Bower.

With this definition, there are two more words we’ll run into that should be clarified:

  • a package is a small, independent piece of reusable code
  • a dependency is a package that your project relies on in order to work

Exploring the NPM Website

Practice: Choosing a NPM Package

On the NPM website, search for these two packages: js-datepicker and date-selector

How would you choose between the two packages that aim to do something similar?

Choosing a Package

Some things to consider when choosing a package:

  • What is the documentation like?
  • Have there been any recent commits? Is the project being maintained?
  • If you look at the GitHub repo for the package, are the issues being worked on?
  • The number of weekly downloads
  • If the package itself has a lot of dependencies, then that could bring on more risk if you then use that package.

Let’s Explore NPM Packages

Start by cloning down the What’s Cookin Starter Kit repo (with the name being replaced by fun-with-npm to keep things separate from your potential project):

git clone fun-with-npm

Change into the fun-with-npm directory and run npm install.

What happened when you ran npm install? What was added to the project?

Adding a New Package

Let’s add a new package:

  1. Go to the npm webpage for is-odd to see how to install it and how to use it within an application. Yes, this package exists even though it seems so simple…
  2. Install a new package called is-odd that checks if a number is odd.
  3. Add a line to your scripts.js file that console logs the result when is-odd checks the number 5.
  4. Edit your code so is-odd checks a string instead of a number.

Now that it’s installed and running, let’s edit the source code!

  1. Go find the is-odd package in the node_modules directory.
  2. In the index.js file for the package, edit the string that gets reported in the error.

Now you can see some of the connection between the source code of a package and your application. Behind the scenes, NPM packages are really just JS files. It’s not too magical.

Let’s Build Our Own

Let’s create our very own package that filters out words based on the number of characters in the word. We’ll call it filter-words.

  1. Create a directory in node_modules called filter-words.
  2. In the filter-words directory, create an index.js file.
  3. In the index.js file, add this code as a boilerplate:
function filterWords() {

module.exports = filterWords;
  1. Import our package into our application (in the scripts.js file), and invoke the filterWords function.
  2. Run the webpack development server to make sure it’s working as expected so far.

Keep Working on Functionality

In your group, wrk on completing the functionality of the filter function using these guidelines:

// filterWords should take in two parameters: the length (number of characters) of the word we want to filter out, and an array of words

// We should be able to use the function like this:

filterWords(3, ['this', 'that', 'hey', 'hat', 'hi'])

// should return ['this', 'that', 'hi']

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