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@siumennel

Node.js Essentials

Posted at

Addition Function

const result = Number(process.argv[2]) + Number(process.argv[3]);
console.log(result);

Working with Timers#1

setInterval(() => {console.log('TCS');}, 5000);

Working with Timers#2

setTimeout(() => {console.log('TCS');}, 2000);

Working with Timers#3

const interval = setInterval(() => {
console.log('TCS');
}, 2000);

setTimeout(() => {
clearInterval(interval);
}, 10000);

Working with callback functions

let sum = 0;
for(let i=0; i<=1000; i++) {
if( i % 3 == 0 ){
sum = sum + i;
}
}

for(let i=0; i<=1000; i++) {
if( i % 5 == 0 ){
sum = sum + i;
}
}
console.log(sum);

read Stream

const fs = require("fs");
var data = "";
const src = fs.createReadStream('Node-stream-handson/data_file.txt', 'utf8');
src.on('data', chunk => {
console.log(chunk.length);
} );

copy stream

const fs = require("fs");
const src = fs.createReadStream('data_file.txt', 'utf8');
src.pipe(
fs.createWriteStream('new_data_file.txt')
);

Explore Modules

var module = require('./module');
var App = require('./App');
const readline = require('readline');
const rs = fs.createReadStream('./input.csv');
//writestreamを作成
const ws = fs.createWriteStream('./output.csv');

const rl = readline.createInterface({
//読み込みたいストリームの設定
input: rs,
//書き出したいストリームの設定
output: ws
});

Events - file systems

const fs = require("fs");
fs.mkdir('Node_folder', (err) => {
if (err) { throw err; }
console.log('testディレクトリが作成されました');
});

// 書き込むデータ準備
const data = "This is Node.js a powerful backend javascript used very widely in industry for developing web applications.";

// 書き込み
fs.writeFile("Node_folder/sample.txt", data, (err) => {
if (err) throw err;
console.log('正常に書き込みが完了しました');
});

Events - http module

var http = require('http');

var server = http.createServer(function(request, response) {
response.writeHead(200, {'Content-Type': 'text/html; charset=utf-8'});
response.end('Hello world');
})

App build - Server Setup

var http = require('http');
var html = require('fs').readFileSync('Sample.html');

var server = http.createServer(function(request, response) {
response.writeHead(200, {'Content-Type': 'text/html'});
response.end('Hello World');
})

server.listen(8000);

App build - Routing

const http = require('http');
var url = require('url');
const server = http.createServer((req, res) => {
var pathname = url.parse(request.url).pathname;
if( pathname == '/hi' ){
res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('Hi Welcome');
res.end();
} else if( pathname == '/hello' ) {

res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('Hello Buddy');
res.end();

} else {

res.writeHead(404, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('404 Page not Found');
res.end();

}

});

const port = 8000;
server.listen(port);

App build - Routing2

const http = require('http');
var url = require('url');
const server = http.createServer((req, res) => {
var pathname = url.parse(request.url).pathname;
if( pathname == '/hi' ){
res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('Hi Welcome');
res.end();
} else if( pathname == '/hello' ) {

res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('Hello Buddy');
res.end();

} else {

res.writeHead(404, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('404 File not found error');
res.end();

}

});

const port = 8000;
server.listen(port);

App build - Posting Data

const http = require('http');
var url = require('url');
const server = http.createServer((req, res) => {
var pathname = url.parse(request.url).pathname;
if (pathname == '/hi') {
res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('Hi Welcome');
res.end();
} else if (pathname == '/hello') {
res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('Hello Buddy');
res.end();
} else {
res.writeHead(404, { 'Content-Type': 'text/html; charset=utf-8' });
res.write('404 Page not Found');
res.end();
}
});

const port = 8000;
server.listen(port);
var http = require('http');
const querystring = require('querystring');

http
.createServer(function (req, res) {
if (req.method === 'POST') {
res.writeHead(200, { 'Content-Type': 'text/html' });
var data = '';

  //POSTデータを受けとる
  req
    .on('data', (chunk) => {
      data += chunk;
    })
    .on('end', () => {
      var form = querystring.parse(data);
      res.end(form);
    });
}

})
.listen(8000);

App build - Handling Requests

var server = require('./server.js');
var routers = require('./routers.js');
var handlers = require('./handlers.js');

App build - https request

// App
const https = require('https');
const fs = require('fs');

const options = {
hostname: 'en.wikipedia.org',
port: 443,
path: '/wiki/Nodejs',
method: 'GET',
};

https
.get(options, (resp) => {
let data = '';
// A chunk of data has been received.
resp.on('data', (chunk) => {
data += chunk;
});

// The whole response has been received. Print out the result.
resp.on('end', () => {
  fs.writeFile('Nodejs.html', data, (err) => {console.log(err)});
});

})
.on('error', (err) => {
console.log('Error: ' + err.message);
});

Events - Working with Custom Events

var events = require('events');
var eventEmitter = new events.EventEmitter();

//Create an event handler:
var Myfunc = function () {
console.log('HI THERE ! HAPPY LEARNING');
}

eventEmitter.on('MyEvent', Myfunc);

eventEmitter.emit('MyEvent');

Events - http module

var http = require('http');
var html = require('fs').readFileSync('Sample.html');

var server = http.createServer(function(request, response) {
response.writeHead(200, {'Content-Type': 'text/html'});
response.end(html);
})

server.listen(8000);

========================

Welcome ! what would you like to have

  • Coffee
  • Tea
  • Milk

Read Stream

var fs = require('fs');
var stream;
readerStream = fs.createReadStream('data_file.txt');

readerStream.setEncoding('UTF8');
readerStream.on('data', (chunk) => {
console.log(chunk.length);
});

Palindrome

function largestPalindrome() {
var arr = [];
for (var i = 999; i > 100; i--) {
for (var j = 999; j > 100; j--) {
var mul = j * i;
if (isPalin(mul)) {
arr.push(j * i);
}
}
}
return Math.max.apply(Math, arr);
}
function isPalin(i) {
return i.toString() == i.toString().split('').reverse().join('');
}
console.log(largestPalindrome());

Evenly divisible number

function findFactor(n, max) {
for (let i = 2; i <= max; i++) {
if (n % i !== 0) return false;
}
return true;
}
let n = 20;
//measuring performance
for (let i = n; true; i += n) {
if (findFactor(i, n)) {
console.log(i);
break;
} else if (i > 1e10) {
console.log('Limit');
break;
}
}

Fibonacci Series\

function sumFibs(num) {
let previous = 0;
let current = 1;
let sum = 0;
let next;

for(current; current <= num;){
next = current + previous;
previous = current;

if(current % 2 === 0) {
  sum += current;
}

current = next;

}

return sum;
}

console.log(sumFibs(4000000)); // return 4613732

largest prime factor

var divisor = 2;
var number = 600851475143;
while(number > 1){
if(number % divisor === 0){
number /= divisor;
} else {
divisor++;
}
}
console.log(divisor); // the largest prime factor of 600851475143

Sum of Squares

const sumSquareDifference = (n) => {
const numbers = [...Array(n + 1).keys()];
const sumOfSquares = numbers.reduce(
(accumulator, number) => accumulator + number ** 2
);
const squareOfSum =
numbers.reduce((accumulator, number) => accumulator + number) ** 2;
return squareOfSum - sumOfSquares;
};
console.log(sumSquareDifference(100));

nth prime number

function getPrimes(max) {
let arr = new Array(max).fill(undefined);
for (let i = 2; i < max; i++) {
if (arr[i] === undefined) {
arr[i] = true;
for (let j = i + i; j < max; j += i) {
arr[j] = false;
}
}
}
return arr.map((item, i) => (item ? i : false)).filter(Boolean);
}
let primes = getPrimes(150000);
console.log(primes[10000]);

Pythogorean triplet

for (var a = 1; a < 500; a++) {
for (var b = a; b < 1000; b++) {
var c = Math.sqrt(a * a + b * b);
if (c > b && Number.isInteger(c) && a + b + c == 1000) {
console.log(a * b * c);
}
}
}

=============================
function isPrime(val){

//test if number is prime
for(var i=2; i < val; i++){
if(val % i === 0){
return false;
}
}
return true;
}

sum Primes

function sumPrimes(num) {
let arr = Array.from({length: num+1}, (v, k) => k).slice(2);

let onlyPrimes = arr.filter( (n) => {
let m = n-1;
while (m > 1 && m >= Math.sqrt(n)) {
if ((n % m) === 0)
return false;
m--;
}
return true;
});
return onlyPrimes.reduce((a,b) => a+b);
}

Sum of Multiples

let sum = 0;
// loop max range
const numRange = 1000;
// common util function for checking multiples
const isMultiple = (num, mode) => (num % mode ? false : true);
// looping over an numbers below 1000 and adding 3 or 5
// multiples to sum
for (let i = 0; i < numRange; i++) { if (isMultiple(i, 3) || isMultiple(i, 5)) sum += i; }
// logs the sum of all the multiples of
// 3 or 5 below 1000 => 233168
console.log(sum);

console.log(sumPrimes(5));

sum Prime

function sumPrime(x) {
var array = [], sum=0;
for (var i=2; i<x; i++) {
if(typeof array[i] === 'undefined') {
array[i]=true;
for(var k = i+i; k<x; k+=i) {
array[k]=false;
}
if (array[i]) {
sum+=i;
}
}
}
return sum;
}

console.log(sumPrime(2000000)); // 142913828922

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