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Node-Solid : Solidify Node Skills

Executing Node Node API Strems Asycn Node

Executing Node

Node overview

• The most popular JavaScript runtime to emerge in the last few years
• Node is used by millions of developers to build web applications
  • Twitter, Facebook, Google, Instagram, etc.
• we can build simple web application to large scale application
• using electron we can build desktop application
• node can also be build hardware embedded application
• build apps end-to-end with one language that is JavaScript

background

• A page is a collection of elements that are rendered on the screen.
  • it consists of HTML, CSS, and JavaScript
  • and DATA from the Server side
• some server side languages to serve data
  • PHP, Python, Ruby, Java, etc.
• Node will allows us to write both client and server side code in one language

node.js features

• Node.js has computer features like accessing files and writing to files
  • it can also access the network
  • it can also access the hardware
  • it can also access the database
• these are c++ specific features that interact with os directly
• when JS works with C++ to control the computer features it is called Node.js

JavaScript Node and Computer

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JavaScript does three things (1 with c++s help)

1. Saves the data and functionality [numbers, strings, objects]
2. Executes the data and functionality
3. Has a way to communicate with the computer using c++ features

• var, let and const are stored in memory
• function are stored in the heap, heap is a large memory space
  • function have a execution context
    • this is the scope of the function and the variables that are in the function
    • the function execution context is created when the function is called its temporary and destroyed when the function is done

Node API

calling Node in JS

• http - is a server side library that allows us to create a server that can be accessed from the internet
• there are 6400 entry points to the http library
• we ask c++ to create a server and then we can access the server from the internet, so we set the port to 80

  const http = require('http'); // require is a function that is used to import a module
  const server = http.createServer(); // create a server
  server.listen(80); // listen to port 80

Calling methods in node

• if we want to run a function to run we pass it in createServer and then we call the listen method
• executeFunction(incomingData, setOutGoingData) a custom function to log to the console

  const http = require('http'); // require is a function that is used to import a module
  const server = http.createServer(executeFunctions); // create a server and execute the logToConsole function
  executeFunction(incomingData, setOutGoingData) {
    console.log(incomingData);
    setOutGoingData().end('Hello World'); // end is a node function that sends the data to the client
  };
 
  server.listen(80); // listen to port 80

calling function under the hood

• node will execute the function and then return the result
• it will also add the arguments to the function
• node automatically create TWO JS OBJECTS FOR US
  • incomingData - the data that is coming in from the client
  • setOutGoingData - the data that is going out to the client
• end - is a node method that will send data to node which will then be sent to client
• setOutGoingData.end('welcome') - will send the data to the client

Q&A

• Q: how do we know what method to use to send data to the client?
• A: we look up node docs and find the method that is used to send data to the client is end
• Q: who do we know we have to use port 80?
• A: 80 is the default port that node will use if we don't specify a port and that is what we are using in the code

Req and Res

• 3 parts of HTTP Req
  • request type - GET, POST, PUT, DELETE
  • headers - meta data about the data that is sent to the server
  • body - the data that is sent to the server

Express

• We have to look into in bound request we have to conditionally answer the request.
• Express is a framework that we can use to create a server that can be accessed from the internet, that helps us set up middle ware that analyzes the inbound request and response
• middle ware patters passes the object through the function and then passes it to the next function to send back the right data
• Express is a web framework that allows us to create a server that can be accessed from the internet
• Express is a node module that we can use to create a server const express = require('express')
• it can be used to create a server that can be accessed from the internet.

  const express = require('express'); // require is a function that is used to import a module
  const app = express(); // create a server
  app.listen(80); // listen to port 80

  app.get('/', (req, res) => { // create a route
    res.send('Hello World'); // send the data to the client
  });

HTTPRequestObject & HTTPResPonseObject

const tweets = [
{ id: 1, text: 'Hello World' },
{ id: 2, text: 'Hello Universe' },
{ id: 3, text: 'Hello Galaxy' },
];
function doThisOnIncomingData(incomingData, functionToSetOutgoingData) {
  const tweet = tweets[incomingData.id];
  functionToSetOutgoingData(tweet);
}
const http = require('http'); // require is a function that is used to import a module
const server = http.createServer(doThisOnIncomingData); // create a server and execute the logToConsole function
server.listen(3000); // listen to port 80

Error Handling in Node

• try - is a block of code that we want to try to run
• catch - is a block of code that we want to run if the try block fails we will change our function doThisOnIncomingData only when there is a request coming in from the client
• server.on - is a method that we can use to listen to a certain event
• events like
  • request - is a event that is fired when a request is coming in from the client
  • clientError - is a event that is fired when there is an error with the client

error handling code

const tweets = [
{ id: 1, text: 'Hello World' },{ id: 2, text: 'Hello Universe' },{ id: 3, text: 'Hello Galaxy' },];
function doThisOnIncomingData(incomingData, functionToSetOutgoingData) {
  const tweet = tweets[incomingData.id];
  functionToSetOutgoingData(tweet);
}
const http = require('http'); // require is a function that is used to import a module
const server = http.createServer();
server.on('request', (req, res) => {
  try {
    doThisOnIncomingData(req, res);
  } catch (error) {
    res.statusCode = 500;
    res.end('Something went wrong');
  }
});
server.on('clientError', (err, socket) => {
  socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
}
server.listen(3000); // listen to port 80

folder structure

• / - is the root folder
• ./ - is the current folder
• ./public/img - current folder and then the folder called public and then the folder called img
• ../ - is the parent folder
• ../../ - is the grandparent folder

JSON object

• JSON is a data format that is used to store data in a file
• JSON.stringify - is a method that we can use to convert a JS object to a JSON string
• JSON.parse - is a method that we can use to convert a JSON string to a JS object

// json object 
const jsonObject = {
  name: 'John',
  age: 30,
  isMarried: false,
};
// convert json object to a string
const jsonString = JSON.stringify(jsonObject);
console.log(jsonString); // {"name":"John","age":30,"isMarried":false}

the FS module

• fs - is a module that we can use to read and write files
• fs.readFile - is a method that we can use to read a file
• fs.readFileSync - is a method that we can use to read a file synchronously

example of reading tweets.json and writing to output.html

const fs = require('fs'); // require is a function that is used to import a module
const tweets = JSON.parse(fs.readFileSync('tweets.json')); // read the file and convert the data to a JS object
const html = tweets.map(tweet => `<li>${tweet.text}</li>`).join(''); // create an array of HTML elements and join them together
fs.writeFileSync('output.html', `<ul>${html}</ul>`); // write the data to a file

Callback Stack, Callback Queue, Event Loop

• call Stack - Js keeps track of the functions that are being called and when they are called, whenever a function is called, it is added to the call stack
• call queue - any function that is delayed from running are added to the call back queue, when the background tasks are done, the functions in the call back queue are called
• Event Loop - Determines what function/code to run next from the queue

Node directory access

• __dirname - is a variable that is set to the absolute path of the current directory
• __filename - is a variable that is set to the absolute path of the current file
• process.cwd() - is a method that is used to get the current working directory
• process.chdir() - is a method that is used to change the current working directory
• process.env - is a variable that is set to the environment variables of the current process
• process.exit() - is a method that is used to exit the process

node response methods

• res.writeHead - is a method that is used to set the headers of the response
• res.sendFile - is a method that is used to send a file to the client
• res.json - is a method that is used to send a JSON object to the client
• res.send - is a method that is used to send a string to the client
• res.end - is a method that is used to end the response