NodeJS
What is NodeJS
- Node.js is a JavaScript runtime built on Chrome’s V8 JavaScript engine.
- Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.
- Node.js’ package ecosystem, npm, is the largest ecosystem of open source libraries in the world.
Callback
-> non-blocking
var fs = require("fs");
fs.readFile('input.txt', function (err, data) {
if (err) return console.error(err);
console.log(data.toString());
});
console.log("Program Ended");
Event
- A main loop that listens for events, and then triggers a callback function when one of those events is detected.
- Another multi-thread environment that execute these events.
All objects which emit events are instances of events.EventEmitter.
var events = require('events');
var eventEmitter = new events.EventEmitter();
// listener #1
var listner1 = function listner1() {
console.log('listner1 executed.');
}
// Bind the connection event with the listner1 function
eventEmitter.addListener('connection', listner1);
var eventListeners = require('events').EventEmitter.listenerCount(eventEmitter,'connection');
console.log(eventListeners + " Listner(s) listening to connection event");
// Fire the connection event
eventEmitter.emit('connection');
eventListeners = require('events').EventEmitter.listenerCount(eventEmitter,'connection');
console.log(eventListeners + " Listner(s) listening to connection event");
Buffer
Buffer provides instances to store raw data similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap.
Buffer class is a global class and can be accessed in application without importing buffer module.
var buf = new Buffer(10);
var buf = new Buffer([10, 20, 30, 40, 50]);
var buf = new Buffer("Simply Easy Learning", "utf-8");
buf.length
buf.write(string[, offset][, length][, encoding])
buf.toString([encoding][, start][, end])
buf[index]
buf.copy(targetBuffer[, targetStart][, sourceStart][, sourceEnd])
Stream
Streams are objects that let you read data from a source or write data to a destination in continous fashion.
Four types of streams.
- Readable - Stream which is used for read operation.
- Writable - Stream which is used for write operation.
- Duplex - Stream which can be used for both read and write operation.
- Transform - A type of duplex stream where the output is computed based on input.
var fs = require("fs");
var data = '';
// Create a readable stream
var readerStream = fs.createReadStream('input.txt');
// Set the encoding to be utf8.
readerStream.setEncoding('UTF8');
// Handle stream events --> data, end, and error
readerStream.on('data', function(chunk) {
data += chunk;});
readerStream.on('end',function(){
console.log(data);});
readerStream.on('error', function(err){
console.log(err.stack);});
console.log("Program Ended");
Npm command
# Mac install location
usr/local/bin/npm
usr/local/bin/node
# Login
npm whoami
npm adduser
# Start a project
npm init --scope=<username>
# Install a module
npm install <modulename>
# Listing dependencies
npm ls
HelloWorld Example
NodeJS
var http = require("http");
http.createServer(function (request, response) {
// Send the HTTP header
// HTTP Status: 200 : OK
// Content Type: text/plain
response.writeHead(200, {'Content-Type': 'text/plain'});
// Send the response body as "Hello World"
response.end('Hello World!');
}).listen(8081);
// Console will print the message
console.log('Server running at port 8081.');
Express
var express = require('express');
var app = express();
app.get('/', function (req, res) {
res.send('Hello World!');
});
app.listen(3000, function () {
console.log('Example app listening on port 3000.');
});
