Node.js Event Emitter

2. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var events = require("events"),
emitter = new events.EventEmitter(),
username = "Eyal",
password = "Vardi";
// an event listener
emitter.on("userAdded", function (username, password) {
console.log("Added user " + username);
});
// Emit an event
emitter.emit("userAdded", username, password);

3. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var events = require("events");
var emitter = new events.EventEmitter();
emitter.once("foo", function () {
console.log("In foo handler");
});
emitter.emit("foo");
emitter.emit("foo");

4. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var events = require("events");
var EventEmitter = events.EventEmitter;
var emitter = new EventEmitter();
emitter.on("foo", function () { });
emitter.on("foo", function () { });
console.log( EventEmitter.listenerCount(emitter, "foo") );

5. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var events = require("events");
var EventEmitter = events.EventEmitter;
var emitter = new EventEmitter();
emitter.on("foo", function (){ console.log("In foo handler"); });
emitter.listeners("foo").forEach(function (handler) {
handler();
});

6. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var events = require("events");
var emitter = new events.EventEmitter();
emitter.on( "newListener" , function (eventName, listener) {
console.log("Added listener for " + eventName + " events");
});
emitter.on("foo", function () { });

7. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com

8. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var EventEmitter = require("events").EventEmitter;
var util = require("util");
function UserEventEmitter() {
EventEmitter.call(this);
this.addUser = function (username, password) {
// add the user
// then emit an event
this.emit("userAdded", username, password);
};
};
util.inherits(UserEventEmitter, EventEmitter);

9. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
function SuperType(name){
this.name = name;
this.colors = ['red', 'blue', 'green'];
}
SuperType.prototype.sayName = function(){ alert(this.name); };
function SubType(name, age){
SuperType.call(this, name);
this.age = age;
}
SubType.prototype = Object.create(SuperType.prototype);
SubType.prototype.sayAge = function(){
alert(this.age);
};

10. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
val getSuperValue
[prototype]
subVal
__proto__
val
__proto__
[prototype]
subVal

11. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
function SuperType(name){
this.name = name;
this.colors = ['red', 'blue', 'green'];
}
SuperType.prototype.sayName = function(){ return this.name; };
function SubType(name, age){
SuperType.call(this, name);
this.age = age;
}
SubType.prototype = Object.create(SuperType.prototype);
SubType.prototype.constructor = SubType;
SubType.prototype.sayAge = function(){
alert(this.age);
};
SubType.prototype.sayName = function(){
return SuperType.prototype.sayName.call(this) + "!!";
};
override
fix constructor

12. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var user = new UserEventEmitter();
var username = "colin";
var password = "password";
user.on("userAdded", function (username, password) {
console.log("Added user " + username);
});
user.addUser(username, password)
console.log(user instanceof EventEmitter);

13. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var fs = require("fs");
var fileName = "foo.txt";
fs.exists(fileName, function (exists) {
if (exists) { fs.stat(fileName, function (error, stats) {
if (error) { throw error; }
if (stats.isFile()) {
fs.readFile(fileName, "utf8", function (error, data) {
if (error) { throw error; }
console.log(data);
});
}
});
}
});

14. © 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var EventEmitter = require("events").EventEmitter;
var util = require("util");
var fs = require("fs");
function FileReader(fileName) {
var _self = this;
EventEmitter.call(_self);
_self.on("stats", function() {
fs.stat(fileName, function(error, stats) {
if (!error && stats.isFile()) {
_self.emit("read");
}
});
});
_self.on("read", function() {
fs.readFile(fileName, "utf8", function(error, data) {
if (!error && data) { console.log(data); }
});
});
fs.exists(fileName, function(exists) {
if (exists) { _self.emit("stats"); }
});
}
util.inherits(FileReader, EventEmitter);
var reader = new FileReader("foo.txt");