Packaging - HackMD

# Packaging What is packaging? Packaging is organizing a related collection of "modules" and code that usually handles one issue. A set of multiple packages is called a "Library". --- ## Dependencies * A dependency is additional code that your program can use. * Dependencies can be libraries, tools, or modules. * You can write your own, or use third party dependencies. * Dependencies save a lot of time and prevents repeating work. --- ### Why not write your own? #### Avoid unecesssary work * Dependencies tend to be large, and even if you know how to create one, it takes a long time. #### Don't try to re-invent the wheel * Dependencies such as popular libraries are well made and maintained therefore using them will merit a smoother program. --- ## Issues with managing dependencies --- #### Managing dependencies is not easy, and especially if you are relying on third party dependencies. Third party libraries often depend on other libraries. This may mean library A depends on C v1.2, and library B depends on C v1.1, meaning A and B are incompatible. --- #### Installing & Updating * Traditionally downloading, installing, and updating dependencies was a tedious manual job. * Dependency Managers aka Package Managers solve this by automating the downloading and installation of dependency packages. --- ### Example for an application with its dependencies Node.js requires the following dependencies to work: | Libraries | Tools | | --------- | ----- | | V8 | npm | | libuv | gyp | | llhttp | gtest | | c-ares | | | OpenSSL | | | zlib | | ** Note: Dependencies can be written in different languages, like the V8 engine is made with C++ by google. --- ## NPM  NPM (Node Package Manager) is software that automates installing, updating, configuring, and removing modules (dependencies), and is one example of a package manager. --- To use npm, first navigate to your package's directory in terminal, and run the following command, and we use '-y' to get the default values in our package.json: > `npm init -y` --- You should now have '`package.json`' in that directory. In order to install a module (dependency) run the following command: > `npm install <module-name>` This installs packages locally and will be stored in ./node_modules. ---  ### What is package.json? This file helps npm identify the project and manage its dependencies. It contains other metadata & properties, but we won't get too into detail. --- ### Global Dependencies The -g flag installs the module globally to your machine, rather than into the node_modules folder of that specific project. > `npm install -g <package-name>` It is not recommended to install packages globally unless you really have to, since it is all stored in the same place and can get messy. --- ### Dev Dependencies Dev Dependencies are modules which are **only** required during development. > npm i --save-dev <package> for short: > npm i -d <package> --save-dev saves it under devDependency in package.json. --- Dev dependencies, unlike regular dependencies, are only needed in the development stage while the latter is also required at runtime. If you **only** need a module for development, it should be strictly added as a ***dev dependency*** to avoid installing unneccesary packages for users. --- ### To use a module in your code: > const module-name = require('module-name'); > > module-name.doSomething(); --- ### To use a module in the terminal: > npm run <command> this will run the command from your "scripts" in package.json --- ### Node modules NPM installs packages in a folder called node_modules in your project's root directory. It is not recommended to share this file with others working on this project, like on Github for example. --- This is where .gitignore comes in to place. .gitignore is a file that tells Git what to ignore and not upload to the repository. To ignore a file, we simply add the file name in .gitignore, separated by a coma: > node_modules, > > another_file, > > and_another_file