npm Package Manager

## Javascript
            ### `npm` Package Manager 
            The best tools have recursive names

---

## Why do we use `npm`?
            1. **Dependency management**: Keeping track of software versions is hard work. npm makes this easier (but it can still be a pain).
            2. **Development and deployment**: Along with Git, npm is often used to manage code on live servers.
            3. **Project collaboration**: Along with Git, npm is used to make sure team members are all developing with the same software versions.

---

### Terminology
 <dl>
 <dt>Dependency</dt>
 <dd>Software that your app needs to function properly. Each dependency will often also have their own dependencies.</dd>

<dt>Package Management System</dt>
 <dd>Software that automates the installation and updating of software dependencies.</dd>

<dt>Semantic versioning</dt>
 <dd>A three number versioning system (<code>major</code>.<code>minor</code>.<code>patch</code> => <code>2.3.1</code>) for software. </dd>
 </dl>

---

<dl>
 <dt><code>Node</code></dt>
 <dd>A framework for running Javascript from the command line or on a server.</dd>

<dt><code>npm</code></dt>
 <dd>npm Package Manager, previously Node package manager (npm is now used for many software projects besides Node)</dd>

<dt><code>npm</code> Package</dt>
 <dd>A package is a file or directory that is described by a <code>package.json</code> file.</dd>
 </dl>

---

### Node in a Nutshell
 - Run a js file from the command line with:
 ```shell
 $ node <path-to-js-file>
 ```
 - Node will not run browser-specific code like `document.querySelector()`
 - We will be using Node in our examples today but it won't be used a lot in this program.

---

### npm Stats and Trivia
            As of July 2019:
            - Largest software package registry in the world.
            - 1 million indexed packages
            - ~10 billion downloads a week
            - ~45 billion downloads a month

---

### npm Security
            - The registry does not have any vetting process for submission.
            - Packages can be low quality, insecure, or malicious.
            - Registry quality is dependant on user reviews and moderation.
            - See: [Notable Breakages](https://en.wikipedia.org/wiki/Npm_(software)#Notable_breakages) (Wikipedia)

---

### npm Outages
            - The npm registry is not distributed. 
            - If the registry goes down, all of npm goes down.
            - See: [npm Status](https://status.npmjs.org/) page for outage history.

---

### Typical npm usage
 1. Initialize a new npm project (or download one).
 ```shell
 $ npm init
 ```
 Or with defaults:
 ```shell
 $ npm init -y
 ```
 2. Install a software package:
 ```shell
 $ npm install <package-name>
 ```
 3. Include the package in your project by following the package's documentation.
 
 ---

## Example `npm` directory structure
            
            ```js
            project-root
            ├── node_modules
                ├── dependency-1
                ├── dependency-2
                └── dependency-3
            ├── app.js
            ├── package-lock.json
            └── package.json
            ```

---

### Important files and directories
 <dl>
 <dt><code>package.json</code></dt>
 <dd>Contains all the meta information about an npm project. If this file isn't present, it's not an npm project.</dd>

<dt><code>package-lock.json</code></dt>
 <dd>An auto-generated list of specific packages and versions that your project uses. Do not edit manually this file.</dd>

<dt><code>node_modules</code></dt>
 <dd>The directory that contains the actual software packages. This can get pretty large.</dd>
 </dl>

---

## Key Takeaways
            - IF your project won't run in the browser, add `node_modules` to your `.gitignore` file. This directory stores all your dependencies (often lots of files) which should not be committed to your repository.
            - Commit `package.json` and `package-lock.json` to your repository (unless you're specifically told not to).
            - You no longer need to use the `--save` flag when installing packages.

---

### Example `package.json` file

```json
            {
              "name": "hello-world",
              "version": "1.0.0",
              "description": "",
              "main": "app.js",
              "scripts": {
                "test": "echo \"Error: no test specified\" && exit 1"
              },
              "dependencies": {}
              "keywords": [],
              "author": "",
              "license": "ISC"
            }
            ```
            See: [Anatomy of a `package.json` file](https://www.digitalocean.com/community/tutorials/nodejs-package-json)

---

## Common Scenarios
            ### Evaluating project status

---

### No `package.json file`
            ```js
            project-root
            └── app.js
            ```

An npm project needs to be initialized with:
            ```shell
            $ npm init -y
            ```

See: [npm - Initialize a new project](https://gist.github.com/acidtone/f2e901fb4b04bd41aa59755e2de9af4f)

---

### No `package-lock.json` and `node_modules`
            ```js
            project-root
            ├── app.js
            └── package.json
            ```

Software dependencies need to be downloaded:

```shell
            $ npm install
            ```

Or install a specific package:
 ```shell
 $ npm install <package-name>
 ```
 
 ---

### Project is ready (maybe)
            ```js
            project-root
            ├── node_modules
                ├── dependency-1
                ├── dependency-2
                └── dependency-3
            ├── app.js
            ├── package-lock.json
            └── package.json
            ```

Common commands to start a project:

```js
            $ npm start
            ```
            ```js
            $ npm run dev
            ```
            ```js
            $ node app.js
            ```

---

### ES `vs` CommonJS Modules
            - There are two competing standards for installing JS modules.
            - CommonJS came first and is the default method in Node.
            - ES Modules came later and is the official browser standard.
            - Browsers only support ES Modules but Node supports both.
            - The current trend is to use ES Modules.

---

### Examples
            CommonJS
            ```js
            const express = require('express');
            ```
            
            - `require()` will not work in the browser.
            
            --- 
            ES Modules
            ```js
            import Reveal from 'reveal.js';
            ```
            
            - `import` will work in Node but the software has to support it.