[Node.js] Level 2 new. Event

Chat Emitter

We're going to create a custom chat EventEmitter.

Create a new EventEmitter object and assign it to a variable called 'chat'.

var chat = new EventEmitter();

Next, let's listen for the 'message' event on our new chat object. Remember to add a callback that accepts the message parameter.

chat.on('message', function(message){

});

Log the message to the console using console.log().

chat.on('message', function(message){
    console.log(message);
});

 

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

var chat = new EventEmitter();
chat.on('message', function(message){
    console.log(message);
});

 

Emitting Events

Read the existing code below and modify it to emit events.

On the chat object, emit the 'join' event and pass in a custom message as a string.

// Emit events here
chat.emit('join', "Hello");

Now emit the 'message' event on the chat object. Just like before, remember to pass in a custom message as a string.

chat.emit('message', "Message: ");

 

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

var chat = new EventEmitter();
var users = [], chatlog = [];

chat.on('message', function(message) {
  chatlog.push(message);
});

chat.on('join', function(nickname) {
  users.push(nickname);
});

// Emit events here
chat.emit('join', "Hello");
chat.emit('message', "Message: ");

 

Request Event

Just like you saw in the video, refactor the HTTP server code to explicitly bind a callback to the 'request' event using the onfunction.

Add an event listener on the server variable that listens to the requestevent. The event listener should take a callback function with two arguments, request and response.

server.on('request', function(request, response){});

Move the logic for handling the request from the http.createServer()callback to your new 'request' event listener. Remember to remove thehttp.createServer() callback once the code has been moved.

var server = http.createServer(function(request, response){
    response.writeHead(200);
    response.write("Hello, this is dog");
    response.end();
});

//change to 
var server = http.createServer();
server.on('request', function(request, response){
    response.writeHead(200);
    response.write("Hello, this is dog");
    response.end();
});

Listening Twice 

Who said you can only listen for an event once?

Add a second 'request' handler to the HTTP server.

server.on('request', function(request, response){});

From inside of the new handler, log the message "New request coming in..." using console.log().

var http = require('http');
var server = http.createServer();

server.on('request', function(request, response){
  response.writeHead(200);
  response.write("Hello, this is dog");
  response.end();    
});

server.on('request', function(request, response){
    console.log("New request coming in...");
});

server.listen(8080);

 

Listening for Close

Like our parents always used to say, listening is more important than talking! Modify the server so that we know when it's closed down.

Listen for the 'close' event on the server. The event listener should take a callback function that accepts no arguments.

server.on('close', function(){});

Inside the 'close' callback, log the message "Closing down the server...".

server.on('close', function(){
    console.log("Closing down the server...");
});

 

var http = require('http');
var server = http.createServer();

server.on('request', function(request, response) {
  response.writeHead(200);
  response.write("Hello, this is dog");
  response.end();
});

server.on('request', function(request, response) {
  console.log("New request coming in...");
});

server.on('close', function(){
    console.log("Closing down the server...");
});


server.listen(8080);