【Node.js】LEVEL 2 - Events

2.2 Chat Emitter

We're going to create a custom chat EventEmitter.

Task 1：
Create a new EventEmitter object and assign it to a variable called 'chat'.

Task 2：
Next, let's listen for the 'message' event on our new chat object. Remember to add a callback that accepts the message parameter.

Task 3：
Log the message to the console using console.log().

```js var events = require('events'); var EventEmitter = events.EventEmitter; var logger = new EventEmitter(); logger.on('message', function(message){ console.log("ERR: " + message); }); ```

2.3 Emitting Events

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

Task 1：
On the chat object, emit the 'join' event and pass in a custom message as a string.

Task 2：
Now emit the 'message' event on the chat object. Just like before, remember to pass in a custom message as a string.

```js 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); }); chat.emit('join', "Hello"); chat.emit('message', "Message:"); ```

2.4 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 on function.

Task 1：
Add an event listener on the server variable that listens to the request event. The event listener should take a callback function with two arguments, request and response.

Task 2：
Move the logic for handling the request from the http.createServer() callback to your new 'request' event listener. Remember to remove the http.createServer() callback once the code has been moved.

```js 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.listen(8080); ```

2.5 Listening Twice

Who said you can only listen for an event once?

Task 1：
Add a second 'request' handler to the HTTP server.

Task 2：
From inside of the new handler, log the message "New request coming in..." using console.log().

```js 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); ```

2.6 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.

Task 1：
Listen for the 'close' event on the server. The event listener should take a callback function that accepts no arguments.

Task 2：
Inside the 'close' callback, log the message "Closing down the server...".

```js 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); ```