# Node js
## Global varibels
1. __filename -> full fill path
2. __dirname -> parent folder full path
3. require -> global function used to import modules
4. module -> info about current module
5. process -> info about current the host device

## Modules
### 1. make your modual
#### _every file is a modual_
1. **export somthing from file**

const somthing = 'somthing';
module.exports = somthing;

2. **import somthing from another file**

const somthing = require('./filepath');

**Full Example**

// at -> file2.js
module.exports = () => {
    for (let i = 0; i < 1000; i++) {
        console.log(`Hello number ${i}`);        
    }
}
-------------------------------------------------
// at -> index.js
const loop = require("./file2");
loop();

**NOTE: when you require a file all code in file will run**
EXAMPLE

// at -> file2.js
console.log("hello world");
module.exports = "test"
-------------------------------------------------
// at -> index.js
const test = require("./file2");

**Terminal**

node index.js
hello world

#### 2. built in moduals
1. OS MODUAL

const OS = require('os');
// info about user 
const user = OS.userInfo()
console.log(user);

// system up time in secound
console.log(`System up time : ${OS.uptime()}`);

2. PATH MODUAL

const path = require('path')
console.log(path.sep);
// out -> \
console.log(path.join("hello" , "world" , "this" , "is" , "a" , "test"));
// out -> hello\world\this\is\a\test
console.log(path.basename('hello/world/this/is/a/test/hello.js'));
// out -> hello.js

3. FS MODUAL
- **sync functions :** stop all tasks until finish this task

const { writeFileSync, readFileSync } = require("fs");

**Example**

const { writeFileSync, readFileSync } = require("fs");
const os = require("os");

// {flag : a} is optional but it tell the node does not override the file just append the new text
writeFileSync("./firstFile.txt", ``)
for (let i = 0; i <= 5000; i++) {
    writeFileSync("./firstFile.txt", `${i}) lorem lorem lorem lorem ${os.EOL}`, { flag: "a" })
}

// second parameter is optional
const text = readFileSync("./firstFile.txt", 'utf-8');
text.split(os.EOL).forEach(el => {
    console.log(el);
});

- **async functions :** do another task will this task are done then when this task

const { readFile, writeFile } = require('fs');
readFile('filePath','utf-8', 
/*call back function*/(error, result) => { console.log(result);})

**Full Example**

const { readFile, writeFile } = require('fs');
writeFile('./firstFile.txt', " lorem", { flag: "a" }, erorr => {
    if (erorr) {
        console.error(erorr);
    }

})

readFile('./firstFile.txt', 'utf-8', (error, result) => {
    if (!error) {
        console.log(result);
    }
})

4. http
**createServer:** this method return a server object
**FULL EXAMPLE**

const http = require('http');

const server = http.createServer();
server.on('request', (request, response) => {
    response.writeHead(200, 'OK', {
        'content-type': 'text/html'
    });
    response.write(`<h1>page : ${request.url.replace('/' , "")}</h1>`);
    response.end()
})

server.listen(5000)

---
## Create package.json file

npm init -y

### Dependencies
is a packages that built by another programers and they are published it in **npm** store and you can use it in your project

**How to install dependencies package ?**

npm i axios

### Devdependencies
is a dependencies that you just need it in development step (you don't need it in production) like **nodemon** package.
**How to install devdependencies package ?**

npm i <package name> (-D or --save-dev)

**Example**

npm i nodemon -D

**Note :** nodemon is a tool that helps develop Node.js based applications by automatically restarting the node application.

### Scripts

"scripts": {
    "start": "nodemon index.js"
}

npm run start

**This will run 'nodemon index.js'**
### uninstall package

npm uninstall packageName

### convert any async function into Promise

const util = require('util');
const { readFile, writeFile } = require('fs');

const readFilePromise = util.promisify(readFile);
const writeFilePromise = util.promisify(writeFile);

const readFileByPath = async (path) => {
    const res = await readFilePromise(path, 'utf-8')
    console.log(res);
    return res;
}

const writeFileToPath = async (path, text, KeepOld = false) => {
    if (KeepOld) {
        const res = await writeFilePromise(path, text, { flag: "a" });
        return res;
    } else {
        const res = await writeFilePromise(path, text);
        return res;
    }
}

writeFileToPath("./helloWorld.txt", "lorem lorem lorem lorem ", true);
readFileByPath("./helloWorld.txt")

**OR YOU CAN GET READ AND WRITE AS PROMISES**

const { readFile, writeFile } = require('fs').promises;

### EVENTS

const Event = require('events');
const myEvent = new Event();

myEvent.on('first_event', () => {
    console.log("Hello World");
})

myEvent.emit('first_event')

### Send data with the event

const Event = require('events');
const myEvent = new Event();

myEvent.on('first-event', (payload) => {
    console.log(`Hello ${payload.name}`);
    console.log(`Your age :${payload.age}`);
})

myEvent.emit('first-event' , {
    name:'abd',
    age:15
})

### Server use Event

const http = require('http');

const server = http.createServer();
server.on('request', (request, response) => {
=    response.end(`page : ${request.url}`)  
})

server.listen(5000)

// :todo createFileStream