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JavaScript Build a Simple Dynamic Site with Node.js Creating a Basic Template Engine in Node.js Making Our Views DRY

Jesse Thompson
Jesse Thompson
10,684 Points
Posted by Jesse Thompson
Jesse Thompson
10,684 Points

Out of curiosity what is the purpose of EventEmitter and util modules?

I dont believe we wrote this code down, I finished the project but I am wondering for usage in my own program.

It seems that usage of util.inherits is discouraged and I just cant make sense of the EventEmitter in the docs. "All EventEmitters emit the event 'newListener' when new listeners are added and 'removeListener' when existing listeners are removed." ???

Why not just parse the data normally as opposed to using this emitter?

profile.js below 

var EventEmitter = require("events").EventEmitter;
var https = require("https");
var http = require("http");
var util = require("util");

/**
 * An EventEmitter to get a Treehouse students profile.
 * @param username
 * @constructor
 */
function Profile(username) {

    EventEmitter.call(this);

    profileEmitter = this;

    //Connect to the API URL (https://teamtreehouse.com/username.json)
    var request = https.get("https://teamtreehouse.com/" + username + ".json", function(response) {
        var body = "";

        if (response.statusCode !== 200) {
            request.abort();
            //Status Code Error
            profileEmitter.emit("error", new Error("There was an error getting the profile for " + username + ". (" + http.STATUS_CODES[response.statusCode] + ")"));
        }

        //Read the data
        response.on('data', function (chunk) {
            body += chunk;
            profileEmitter.emit("data", chunk);
        });

        response.on('end', function () {
            if(response.statusCode === 200) {
                try {
                    //Parse the data
                    var profile = JSON.parse(body);
                    profileEmitter.emit("end", profile);
                } catch (error) {
                    profileEmitter.emit("error", error);
                }
            }
        }).on("error", function(error){
            profileEmitter.emit("error", error);
        });
    });
}

util.inherits( Profile, EventEmitter );

module.exports = Profile;

`
Justin Deardorff
Justin Deardorff
8,448 Points
Justin Deardorff
Justin Deardorff
8,448 Points

I hate to fire off documentation but you should find what you are looking for in here: https://nodejs.org/api/events.html

1 Answer

Jeremy Ashcraft
Jeremy Ashcraft
14,786 Points
Jeremy Ashcraft
Jeremy Ashcraft
14,786 Points

I've only started studying node since yesterday, but as far as i understand: EventEmitter is a class with many event related methods. the .emit() method lets you create a custom event. with the .emit() method you can give it a custom name, and choose what data to send along to the listener with the event when triggered. you can then set a listener for this event. the listener executes a callback function using the data passed to it via the .emit() method.