Understanding of NPM

What is NPM?

• Node Package Manager.
• NPM is a necessary tool to manage Node.js project.
• Online Storage + Command Line tool

What is NPM Online Storage?

• It is a place for numerous open source libraries and tools to be uploaded.
• We can easily search libraries and tools we need.
• It has a big ecosystem

What is Command Line Tool?

• We can Install tools and libraries from online storage using command line tool.
• We can also set up and manage our project.
• We can manage dependencies for our project.

Let's use NPM

What does "use NPM" mean?

• It means we learn how to use command line tool.

Create Project

npm init

• This command creates a project directory
• In the directory, It makes package.json file after some of questions.
• This project directory is Node.js project.

What is package.json?

• It is a file that information associated with project is saved.
• We can remote this file directly or by npm command line.

package.json's components

• version : project version.
• name : project name.
• description : project description.
• scripts : It is a custom script we can run by "npm run [script name]" command.
• dependencies
• devDependencies : Dependencies only used in development environment.

Dependency Management

• It is a way to manage dependencies used in our project.
• Because we are relying on many libraries, We say these libraries are "dependency".

What is library?

• This chunk of code operates specific functions.
• We use complicated functions we need from other people's code of online storage.
• library is called "package" in Node.js

Let's install packages from online storage!

Add & Download dependency

npm install [package-name]

• We can add packages we need.
• Added packages are added in dependencies of package.json file.
• library code is saved in node_modules.

Dependencies and devDependencies

npm install [package-name] --save-dev

• We can separate dependencies for development environment from production environment.
• dependencies for development environment are added in devDependencies of package.json file.

package-lock.json

• This file fixes the version of packages in dependencies.

Version Notation

npm install [package-name]@[version]

• ~1.13.0 -> installl version 1.13.x
• ^1.13.0 -> install version 1.x.x
• 0.13.0 -> install 0.13.0

Download all Dependency

npm install

• This command download packages defined in package.json.

Download production dependency

npm install --production

Add global packages.

npm install [package-name] --global

Local package and Global package

• Local package : packages declared in package.json file and saved in node_modules
• Global package : packages installed by "npm install -g" command and saved in global package stoage in our computer.

What should we use between local and global package?

• For the good management of our project, We should use local package.

Remove dependency

npm remove [package-name]

• We can remove dependency package.
• This removes packages from dependencies and devDependencies of package.json file and node_modules folder.

Execute Script

• package.json

• run

• Script is code that operates simple behaviors.

• It is declared in package.json
• We can run the script in package.json using "npm run [script-name]"

Why do we use npm script?

// 1
"scripts" : {"test" : "node_modules/.bin/tap test/\*.js"}

//2
"scripts" : {"test" : "tap test/\*.js"}

• We don't have to write where node_modules folder is. We can just access to packages easily like number 2

Common Scripts

• test : unit test
• start : project start
• stop : project stop

NPM Summary

• npm init : Create project
• npm install : Add dependencies
• npm remove : remove dependencies
• npm run : run script
• node_modules directory : Directory that chunks of packages are saved.
• package.json file : project management (Version, dependencies..)
• package-lock.json : Check dependency version.

NPX

What is NPX?

npm i cowsay -g
cowsay hi

npx cowsay hi

// We can choose specific node.js version
npx node@12 index.js
npx node@14 index.js

• This is a tool we can use npm package without installing it.
• We can execute npm package right way not adding the packages to our project and global package storage.

Execute code in github gist

npx https://gist.github.com/zkat/4bc19503fe9e9309e2bfaa2c58074d32

Node.js Module

What is Module?

• Module is a solution to split code into separate functions.

• We separate B code as a module because It is reused in all codes.

Module and Packages

• A chunk of modules is a package
• So npm packages are having a chunk of many modules.
• package > module

Default Provided module in Node.js

console

// Express log level
console.log();
console.warn();
console.error();

// time trace
console.time();
console.timelog();
console.timeEnd();

Process

• This provides arch, argv, env associated with execution environment.
• This also provides abort, kill, exit associated with process behavior.

fs

• We use this for file input and output.
• readFile : read file, writeFile : write file
• Provide Sync function for synchronous operation.
• Detect file/directory changes using watch.

http

• We use this for http server and client.
• Create server using createServer function.
• Create http request using Request function.

Writing and Use of Module

How to declare module in code?

const name = ‘elice’;
const age = 5;
const nationality = ‘korea’;
module.exports= { 
  name, 
  age, 
  nationality ,
};
---
const student = require(‘./elice’);
// print student -> { name: ‘elice’, age: 5, nationality: ‘korea’}

Basic writing of module

module.exports= { 
  name, 
  age, 
  nationality ,
};

Writing module by variable name

constname = ‘elice’;
constage = 5;
constnationality = ‘korea’;

exports.name = name;
exports.age = age;
exports.nationality = nationality;

How to export a function?

module.exports= (name, age, nationality) =>{
  return { name, age, nationality,};
}
---
const student = require(‘./elice’)(‘elice’, 5, ‘korea’) ;
// print student -> { name: ‘elice’, age: 5, nationality: ‘korea’}

• We can make a module a function.
• So we can give arguments to modules when we declare the module.

How to use module?

require("module path");

const dayjs = require("dayjs"); // npm package
console.log(dayjs());

const myModule = require("./my-module"); // my-module/index.js
console.log(myModule);

const myFunctionModule = require("./my-function-module"); // call functional module
console.log(myFunctionModule(name, age, nationality));

How to call Json file?

const myDataa = require("./my-data");
console.log(myData);

• Json files are parsed into object automatically.