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📕 workshop-webgl-glsl → Intro to Node.js and npm

Intro to Node.js and npm

Node.js is a software that allows us to run JavaScript files and programs from the terminal.

npm is what we will use to download JavaScript "modules" (pieces of code) and command-line tools.

Contents

Installation

Install the latest version of Node.js (v10 is recommended, v12 is also fine) from their website. This also comes bundled with a recent version of npm.

After installation, you should be able to open your Terminal window (see the Command Line) and run the following:

# print node version
node -v

# print npm version
npm -v

If both commands work and give you a number, then it means the tools installed correctly.

Node REPL

A handy thing is to enter the Node REPL (Read, Eval, Print Loop) which allows us to run JavaScript from within our Terminal window.

Just run the node command and it will enter the REPL:

node

Now you can enter JavaScript expressions like 2 * 3, const a = 3, console.log("hello"), and so on.

To quit the REPL, enter Ctrl+C.

💡 Since we are in a "Pure JavaScript" environment without P5.js, we don't have access to its utilities like sin(), PI, random(), and so on. However, many of these exist natively in JavaScript in the Math object.

Running JavaScript Files with Node.js

Next, let's create a new JavaScript file that prints the current time.

First, create an empty directory and then an empty JavaScript file:

# create an empty directory
mkdir MyProject

# go into the directory
cd MyProject

# create an empty file within it
touch index.js

Now open the file in a text or code editor and paste in the following:

console.log(new Date());

Now, when we run node index.js, it will execute the script as if it were a command-line application.

node index.js

Result:

Modules and require()

Unlike in the browser, in Node.js we can import "modules" of code into our programs. These are small pieces of code that other people have written, and using them generally makes our lives easier.

Let's do something simple and require the 'url' module, which is built-in to Node.js and provides utilities for dealing with URL strings.

We use the require(moduleName) function to import modules. Let's update our index.js with the following:

const URL = require('url');

const parts = URL.parse('http://google.com/');
console.log(parts);

Now when we re-run our program with node index.js, it will result in the following:

Another commonly used built-in module is fs which gives us the ability to read and write files in JavaScript. Here is an example:

const fs = require('fs');

// Assuming myfile.txt exists in the working directory
const txt = fs.readFileSync('myfile.txt').toString();

// Print the file, maybe do something with it...
console.log(txt);

Installing Modules from npm

Things start to get interesting when you install and use modules from npm. There are over a million packages on npm, and hundreds of thousands of really useful and fun pieces of code.

Step 1: Creating a package.json

Before we can use modules from npm, we have to make sure we have a package.json file in our folder. This file holds all the modules we've installed.

If you are in the same empty folder that you created index.js, then you can run the following to generate a simple package.json file:

npm init -y

You only need to do this the first time you create a new project.

Step 2: Installing Modules Locally

Now that you have a package.json file, you can install modules from npm.

Here is a fun one: superheroes is a module that gives you a list of ~1800 superhero names like "Spider-Man" and "T'Challa".

To install it, we will use npm in our terminal, in the same folder as before:

npm install superheroes

This will update package.json automatically.

Now we can require('superheroes') in the REPL or in a JavaScript file. Here's a simple program that pits two random superheroes against each other:

const superheroes = require('superheroes');

const a = superheroes.random();
const b = superheroes.random();
console.log(a, 'vs.', b);

Each module might be used in a slightly different way, typically if you consult the module page on GitHub or npm it will include code examples and documentation.

There are modules on almost every topic, here's a few cool ones:

  • twitter — Node.js access to the Twitter API
  • philips-hue — Connect with Philips Hue bulbs via Node.js
  • johnny-five — Connect with hardware interfaces, LEDs, robots and more with Node.js
  • pdfkit — Generate PDF files in Node.js
  • brain.js — Machine learning in JavaScript
  • jimp — image manipulation with Node.js
  • neat-csv — parse CSV files with Node.js
  • franc — detect the language of a given string

Installing Applications from npm

Not only can you install small libraries of code from npm, but you can also use it to install command-line applications.

To install a CLI application, we use the --global flag when installing. You can run this command from any folder, and you don't need a package.json file for global applications.

For example, let's install serve now, which will allow us to develop HTML websites without the internet:

npm install serve --global

💡 If you run into EACCESS errors, see the next section

After its installed, we should be able to run serve from the command-line. Use a dot . as the path, which means "current directory."

serve .

Now try opening http://localhost:5000/ (or whatever URL is printed) in your browser to see the result. If you add an index.html in your folder and then reload the browser, you can start to develop a simple website.

Here's an example index.html file you can use:

<p>Hello <b>world!</b></p>

Troubleshooting EACCESS Errors

If you get an EACCES error when installing something with --global, you can try one of the following ways to fix this:

(Quick Hack) Use sudo

A quick way to fix is with sudo, but this is generally not recommended as it can be less secure/safe! ⚠️

sudo npm install serve --global

Follow the steps below for a more secure approach to globally installing CLI tools from npm.

Reinstall Node.js

Sometimes reinstalling Node.js (perhaps a different version than you last tried) will resolve the issue. After installing, quit your terminal and reboot your computer.

Then try installing a global module again like so:

npm install serve --global

(macOS Only) Change Default Directory

If the above doesn't fix it, you can try the following on macOS.

Run each of these commands in your terminal window one after another:

mkdir ~/.npm-global

Then:

npm config set prefix '~/.npm-global'

Now we need to add a line to a file called ~/.profile. First make sure the file exists:

touch ~/.profile

Now we will append a line to it. First, copy the following line exactly with ⌘+C:

export PATH=~/.npm-global/bin:$PATH

Now, we will edit the file via terminal, run the following:

sudo nano ~/.profile

This will prompt for your computer's password, type it in and hit Enter.

Then it will open the file in the Terminal window. The file may already have some text in it, so we will scroll down by pushing the Down arrow key until you cannot scroll down any more.

Now hit ⌘+V to paste the line we copied earlier line into the file.

Then hit Ctrl+O to save the file, and then Enter to confirm.

Then hit Ctrl+X to exit the text editor.

Finally, we can run the following terminal command:

source ~/.profile

And we should be able to re-install npm modules globally:

npm install serve --global

Node Version Manager

If you still can't get it to work, you may need to install a Node Version Manager:

  • macOS – nvm
  • Windows – nvm-windows (download and unzip nvm-setup.zip)

Once its installed, quit and re-open your terminal and you should be able to run it like so:

nvm --version

Now run the following to install latest Node.js:

nvm install stable

And fianlly we alias it so that it persists every time we close and reopen our terminal:

nvm alias default stable

Now try re-installing your CLI app globally from npm:

npm install serve --global

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