Travis Horn
Travis Horn

Travis Horn

The Basics of Modular JavaScript & npm Packages

The Basics of Modular JavaScript & npm Packages

Travis Horn's photo
Travis Horn

Published on Aug 10, 2016

6 min read

One of the biggest jumps a new JavaScript developer can make is going from writing collections of spaghetti code to using a system of loosely coupled modules, where each module has a particular task and can be included in any project where it is needed.

I will break down the process of using and writing JavaScript modules into these five steps. Feel free to skip some if you are already comfortable with them.

  1. Installing Git (on Windows)

  2. Installing Node.js (on Windows)

  3. Using npm packages in Node

  4. Using npm Packages in the browser

  5. Creating your own modules

Photo by [Erwan Hesry](https://cdn.hashnode.com/res/hashnode/image/upload/v1627410508402/MSDoSaUAD.html)Photo by Erwan Hesry

1. Installing Git on Windows

There are many options for installing and using Git. On Windows, I recommend installing the GitHub desktop app, which has Git bundled with it. With the GitHub desktop app, you will be able to easily publish any modules you make to the open source community and allow others to access, modify, and collaborate on your modules.

Creating a GitHub account

  1. Go to https://github.com/

  2. Enter a username, your email address, and a password of your choosing

  3. Click the Sign up for GitHub button

Installing the software

  1. Go to https://desktop.github.com/

  2. Click Download GitHub Desktop

  3. When the .exe finishes downloading, double-click it

  4. Follow the guided installation instructions

  5. Open the application and sign in with your GitHub account

2. Installing Node.js on Windows

There are also many ways to install Node.js. Each have their benefits. The easiest way to get up and running is the official Node.js binary for Windows.

  1. Go to https://nodejs.org

  2. Click the green download button for the latest or LTS version. While either one is honestly fine, I usually stick with the LTS version at the cost of not being on the bleeding edge.

  3. Once the .msi file has been downloaded, double-click it and follow the installation instructions

  4. Open a Command Prompt and run node -v to make sure it works

> node -v
v4.4.7

3. Using npm packages in Node

Once you start breaking your apps into smaller modular packages, you will find that, in so many cases, someone has already had the same need as you and has already written a package for it. In the JavaScript world, the main repository for all of these packages is npm. First, let’s see how to use these packages in Node, then we’ll see how you can also use them in the browser.

Setup

First, make sure you have Node installed.

Then, when creating a new project…

  1. Open a Command Prompt and cd into the folder you are working in

  2. Run npm init and answer each question about your project

> mkdir mypackage
> cd mypackage
> npm init

name: (mypackage)
version: (1.0.0)
description: My first npm package
entry point: (index.js)
test command: 
git repository:
keywords:
author: Travis Horn
license: (ISC) MIT

About to write to C:\code\mypackage\package.json:

{
  "name": "mypackage",
  "version": "1.0.0",
  "description": "My first npm package",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Travis Horn",
  "license": "MIT"
}

Is this ok? (yes)

This will create a package.json file that contains metadata about your project.

Installing a package

When you find a package that you want to use, just run

npm install [package name] --save

This installs the package and saves it as a dependency in package.json.

npm install lodash --save

package.json:

{
  "name": "mypackage",
  "version": "1.0.0",
  ...
  "dependencies": {
    "lodash": "^4.14.1"
  }
}

Using a package

Once it is installed, just require it at the top of any script that uses it, like so:

var _ = require('lodash');

You now have access to the _ object, which contains all the code downloaded and installed with the package.

var myObj = _.assign({ 'a': 1 }, { 'b': 2 }, { 'c': 3 });

// myObj = { 'a': 1, 'b': 2, 'c': 3 }

4. Using npm packages in the browser

Using packaged modules like that in Node is great. But what about the browser? Like everything else I’ve mentioned, there are many ways to get this done. One simple option is browserify.

Setup

Open a Command Prompt and run

npm install -g browserify

This will install browserify globally. Meaning that it’s not tied to a specific project, but rather a utility that you can use anywhere.

Installing a package

When you find a package you want to use, just run

npm install [package name]

Using a package

First, require it at the top of any script that uses it, like so:

var _ = require('lodash');

You now have access to the _ object, which contains all the code downloaded and installed with the package. Before running in the browser, you need to bundle your code with browserify

  1. Run browserify [filename].js -o bundle.js. Remember to replace [filename] with the filename of the script you wrote.

  2. Include the bundle in your HTML with `

5. Creating your own modules (npm packages)

There may not be a module out there that does what you want to do. In this case, it’s a good idea to write your own module that you can re-use any time you need it. You can even publish it to the world (using npm) and help other people if you wish.

A good module is well tested, so I’ll show you how to write a module with tests.

  1. Open the GitHub desktop app and create a new repository by clicking the plus icon, entering a project Name and Local path, choosing Node from the Git ignore dropdown box, and clicking Create repository

  2. Open a Command Prompt and cd into the repository’s directory

  3. Run npm init and answer each question about your project

  4. Run npm install mocha chai — save-dev

  5. Create test.js and write testing like Fig 1

  6. Modify package.json scripts to include a test script like Fig 2

  7. Write your module in app.js. A single object will need to be exported with module.exports like Fig 3

  8. Run npm test and make sure everything is passing. If not, modify code to pass tests

  9. Write README.md with a description, installation instructions, usage, how to run tests, and a software license

  10. Commit changes in the GitHub desktop app by clicking the Changes tab, entering a summary of changes, and then clicking Commit to master

  11. Optional — push to GitHub (online site) by clicking Publish and then clicking Publish [name]

  12. Optional — publish on npm by running npm publish in the command prompt

Fig 1

require('chai').should();
var pkg = require('./app');

describe('pkg', function() {
  it('adds two numbers', function() {
    pkg.add(1, 1).should.equal(2);
  });
});

Fig 2

"scripts": { "test": "mocha --reporter spec tests" }

Fig 3

module.exports = {
  add: function(num1, num2) {
    return num1 + num2;
  }
};

The methods I used in these steps are only one way of doing it. You will undoubtedly develop your own style and figure out what tools work best for you. Hope fully this post will give you a head start.

 
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