In this lab we will be exploring the node CLI and the concept of a javascript "package" or "module".

This tutorial assumes you have node installed on your computer.

"R.E.P.L." stands for "Read Evaluate Print Loop". The Chrome Javascript Console is an example of a REPL.

From the command line, type node. This will launch the node REPL. Type .exit to quit.

$ node

> 1 + 1;
2
> "hello" + "world";
"helloworld"
> .exit

The keyboard shortcut ctrl+c is your friend! Node will only evaluate syntactically correct code (e.g. all your brackets match). If you forgot to close a bracket, you will see ... when you hit enter. Here are your options:

• Hit ctrl+c to start over if the mistake in on the line above.
• If your current code is correct, keep typing and complete your thought.

$ node

> function bad({
...                     # Uh oh! Super broken code. Hit ctrl+c to start over!
>
> function good(){
... return "yay";
... }                   # oops, almost forgot to close my curly bracket!
undefined
> good();
"yay"
> .exit

The core javascript library has a lot of cool features, but it doesn't do everything. When we want more powerful tools, or have a domain-specific problem, we generally get help from third-party libraries and frameworks.

Jargon Note: The words "Package", "Module", and "Library" are used interchangably.

For example the library Lodash has a bunch of convenience methods that make working with arrays easier.

Using the lodash .last() method we can grab the "c" in the following array:

> var lodash = require("lodash"); // import the lodash library into the REPL
> lodash.last(["a", "b", "c"]);
"c"
> .exit

BUT WAIT! We need to download the lodash package first!

From inside your project directory:

$ npm -v
2.3.0       # Make sure you have node >= v2.3.0

$ npm install --save lodash
# wait for it to install
$ ls
# README.md node_modules

Now your project directory has a new folder in it called node_modules and our first package "lodash".

    .
    ├── README.md
    └── node_modules
        └── lodash
            ├── LICENSE
            ├── README.md
            ├── index.js
            ├── last.js
            ├── /... and many more files .../

Question: What do you think is in lodash/last.js? (Take a look!)

When you want to include third-party packages in your project as "dependencies", you need to list which versions of packages you're using. To make this easier, npm stores this information in a json object called package.json.

To generate this file, type npm init and then follow the prompts. (Hit Enter to accept the default option):

    name: (build-your-own-node-package) sillyipsum
    version: (1.0.0) 
    description: A silly fake data generator, a la lorem-ipsum.
    entry point: (index.js) 
    test command: 
    git repository: 
    keywords: 
    author: janedoe
    license: (ISC) MIT
    About to write to /path/to/build-your-own-node-package/package.json:

    {
      "name": "sillyipsum",
      "version": "1.0.0",
      "description": "A silly fake data generator, a la lorem-ipsum.",
      "main": "index.js",
      "dependencies": {
        "lodash": "^4.17.4"
      },
      "devDependencies": {},
      "scripts": {
        "test": "echo \"Error: no test specified\" && exit 1"
      },
      "author": "janedoe",
      "license": "MIT"
    }


    Is this ok? (yes)

You should see "lodash" listed as dependency in your project.json.

You're going to be using a ton of third-party libraries and frameworks, so over time your node_modules folder can get pretty big. Let's tell git that it's okay to ignore our node_modules folder. All of our dependencies are listed in package.json, so it's easy for another developer to get up and running (all they have to do is type npm install and node will take care of the rest).

Right now if you type git status it will list the node_modules folder, and we don't want that. To fix this:

1. Open .gitignore in your text editor.
2. Add a the word node_modules on a new line. Don't forget to save!
3. Now when you type git status you will see that node_modules is no longer listed.
4. Now we're ready to git add and git commit!

    git add .gitignore
    git commit -m "ignored node_modules
    git add package.json
    git commit -m "added package.json, lodash dependency"

• Open and close the node REPL.
• Open the REPL and make a syntactical mistake (e.g. [{])). How do you recover?
• Import the lodash library into the REPL.
  • Are you sure you imported it?

Let's create our first module, a silly lorem-ipsum style fake data generator!

mkdir sillyipsum
touch sillyipsum/index.js
touch sillyipsum/test.js

Add this to index.js:

module.exports
module.exports.shakespearianInsult = function() {
    return "You villainous tickle-brained barnacle!";
}

Now open your node REPL:

$ node
> var insultMe = require("./sillyipsum/index.js");    // THESE ARE THE SAME
> var insultMe = require("./sillyipsum");             // THESE ARE THE SAME
> insultMe();
"You villainous tickle-brained barnacle!"
> .exit

Note: The dot+slash at the beginning of "./sillyipsum/index.js" instructs node to look in the current directory!

Another way to execute your code is to use the test.js file.

Add the code from above to test.js:

var insultMe = require("./sillyipsum");
var output = insultMe();

console.log(output);

To execute this code from your command line, type:

$ node path/to/sillyipsum/index.js
"You villainous tickle-brained barnacle!"
# or
$ node path/to/sillyipsum
You villainous tickle-brained barnacle!

Note: When we name a file index.js or index.html we are indicating that it is the "main" entry point for the program. This makes it easy for developers (and programs!) to know exactly which file to run. That's why we can say require("./sillyipsum") and can skip the index.jspart. This is true for hostedindex.html` files too!

Can you extend your sillyipsum module to include methods for generating fake data? Here are ideas:

• loremIpsumSentence() - A single lorem ipsum sentence.
• loremIpsumSentence(3) - 3 lorem ipsum sentences.
• random() - A random number between 1-100;
• random(0,10) - A random number between 0 and 10;
• state() - A random state name.
• city() - A random city name.
• streetAddress() - A random street address.
• fullAddress() - A full address (city, state, street).
• The sky is the limit!

• NPM's guide to [Installing Packages])https://docs.npmjs.com/getting-started/installing-npm-packages-locally)
• NPM's guide to Using package.json