Hello World in Node.js - Part 2 - NPM

Node.js comes with a helpful utility tool, Node.Js Package Manager(NPM). NPM is used to manage your dependencies. But NPM is not just for dependencies, it can be used to create and run custom commands against your project like testing, starting server, etc. You can also install other helpful tools and utility programs globally in your system.

In Part 1, we created the index.js file and ran it with node index.js command in terminal. Along with it, we are also going to create a new file package.json. Let’s create a new folder and move the index.js file into it. Now create package.json file with it.

Package.json

package.json file contains all the metadata about our project. It describes our project, like who created this project, what’s the current version, license, etc. But the most important use of package.json file is defining dependencies for our project. The advantage using package.json file is that you can take your code anywhere and use npm to install all the dependencies.

A Sample package.json file looks like this

{
  "name": "npm_intro",
  "version": "1.0.0",
  "description": "An introduction to NPM",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [
    "introduction",
    "tutorial",
    "npm"
  ],
  "author": "Suyash Mohan",
  "license": "ISC"
}

More about package.json can be read here.

You can create this file yourself in your editor or use npm init command in terminal. I prefer using npm init command. It will ask you default values for all the above fields and save it as package.json file. The above file was created using npm init command only.

Packages

The strength of NPM comes from its vast list of packages created by the community.

In our example, we console logged “Hello World”. But that is boring. Let’s give color to our message. We don’t have to go crazy and write all the logic our self to figure out how to print a message in color. We are going to use a very helpful package named chalk.

To add chalk to our dependency list, we can either type it out ourself in package.json file or use the following command

npm install --save chalk

This will download the chalk package. The --save flag also saves this information in our package.json file. All packages are downloaded and stored in node_modules folder. Our directory should look like this

├── index.js
├── node_modules
|  ├── ansi-regex
|  ├── ansi-styles
|  ├── chalk
|  ├── escape-string-regexp
|  ├── has-ansi
|  ├── strip-ansi
|  └── supports-color
└── package.json

Wait a minute! We installed chalk what all are these folders in node_modules. These are the dependencies being used by chalk package. That’s how npm manages all the dependencies.

Our package.json file will now look like this.

{
  "name": "npm_intro",
  "version": "1.0.0",
  "description": "An introduction to NPM",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [
    "introduction",
    "tutorial",
    "npm"
  ],
  "author": "Suyash Mohan",
  "license": "ISC",
  "dependencies": {
    "chalk": "^1.1.3"
  }
}

Now our package.json contains dependencies section and dependency chalk package in it. ^1.1.3 is the version of chalk being used. This ensures, our project will always use this version, reducing the chance of incompatibility with the future version. You can, of course, change the version to your choice.

Scripts Section in package.json

The scripts section in package.json is a very powerful feature. We can define custom commands to execute with npm command. For example:

"scripts": {
    "start": "node index.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  }

Now we can call npm start or npm run start to execute our start script instead of calling node index.js.

Installing global packages.

Another important use I found about NPM is to install utility programs or tools available on NPM’s registry. Once installed globally, these programs become available independent of your project.

I have created a tree structure for our project. I didn’t this by hand because I don’t have to. I found a great tool on NPM - tree-cli which can be used to create tree diagrams for any structure. To install it, I ran the following command

npm install -g tree-cli

If you are on Mac OS or Linux, you might need to run it with sudo command if you don’t have root access. tree-cli gave me tree command. I can run tree command in any directory in my terminal to produce tree structure of it like this:

tree -l 2

Phew!!! It was a lot of stuff. If you have any doubt/advice please put it in the comments section.

Next

Continue to Part 3 to get started with Express.js and create your first server.