Nodejs (I) event driven programming

Node.js Use a large number of events , That's why Node.js One of the reasons why it is faster than other similar technologies . When Node Start its server , You can simply initialize its variables , Declare functions , Wait for the event to happen .

Although the event seems to be similar to a callback . The difference is that the callback function returns the result asynchronously , Event handling works in observer mode . Listen to the event function as an observer . Whenever an event is dismissed , Its listening function starts to execute .Node.js There are multiple built-in Events . The main actors are EventEmitter, You can use the following syntax to import .

var events = require('events');// Add a reference to the event module 
//create an eventEmitter object Create an event emitter object 
var eventEmitter = new events.EventEmitter();

//create a function connected which is to be executed 
//when 'connection' event occurs
// Create a connected function to execute 
//“connection” Event time 
var connected = function connected() {
   console.log('connection succesful.');
   // fire the data_received event  Start data receiving event 
   eventEmitter.emit('data_received');
}

// bind the connection event with the connected function Bind the connection event to the connected function 
eventEmitter.on('connection', connected);
 
// bind the data_received event with the anonymous function
eventEmitter.on('data_received', function(){
   console.log('data received succesfully.');
});

// fire the connection event 
eventEmitter.emit('connection');

console.log("Program Ended.");// 

eventEmitter.on('connection', connected); Connect events connection And connected Function binding , When executed eventEmitter.emit('connection'); Trigger the event to execute the corresponding function