How to write and publish your first NPM package

Before we begin…

Before we begin this, you should have the following things set up.

GitHub account
NodeJS and npm installed
npm account

Choosing a package name

You need to check whether the name is available for the npm package. If you are publishing unscoped (public) package; the name of the package should be unique.

However, if you are publishing a scoped (private) package then name does not have to be unique and name takes the format of @npm_username/package-name
Read more on

Initializing the npm package

Create a new directory and initialize using npm init

$ npm init

Initializing package will ask you a few questions for setup.
The default package.json file will be created in your project directory

{
  "name": "number-to-comma-format",
  "version": "1.0.0",
  "description": "Convert a number to comma separated format",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "RAJESH K",
  "license": "MIT"
}

Create the Node module

The main field in package.json defines the entry point of your package.

Let's create index.js file

$ touch index.js

Add the following code to index.js

'use strict'

const defaultOptions = {
  minimumFractionDigits: 2,
  maximumFractionDigits: 2
};

/**
 * @param  {Number} num - Number to be converted
 * @returns - Formatted number format
 */
function formatNumberToComma(num) {
  return Number(num).toLocaleString('en', defaultOptions);
}

module.exports = formatNumberToComma;

Add a README

It's a good idea to include documentation for your package so others know how to use it
Generally, a README should cover

Description of what your package does
Installation and usage instructions
Example code
Contribution guidelines
License used by the package Choosing the right license

Test your package locally

It is recommended to test your package locally before publishing to npm

Create and initialize new project outside package directory
Package can be installed by the following command

npm install number-to-comma-format

The problem with this is that your package is still not published yet so it isn't in npm. You need to reference your package locally while developing and testing it.
You could install the package using an absolute path to the package.

npm install /home/rajesh/dev/number-to-comma-format

Initialize Git

Create a new repository in github for your package and push the source code to git

git init
git add .
git commit -m "Initial commit"
git remote add origin https://github.com/rajeshkumaravel/numbertocommaformat.git
git push origin master