Node.js Event Emitter
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The document discusses using Node.js events and the EventEmitter class. It shows examples of creating EventEmitters, adding event listeners, emitting events, checking the number of listeners, and emitting events to all listeners. It also shows an example of creating a class that inherits from EventEmitter to add event-driven functionality for reading a file.
![© 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);
};](https://image.slidesharecdn.com/02-eventemitter-140721230507-phpapp02/85/Node-js-Event-Emitter-9-320.jpg)
![© 2014 All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
val getSuperValue
[prototype]
subVal
__proto__
val
__proto__
[prototype]
subVal](https://image.slidesharecdn.com/02-eventemitter-140721230507-phpapp02/85/Node-js-Event-Emitter-10-320.jpg)
![© 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](https://image.slidesharecdn.com/02-eventemitter-140721230507-phpapp02/85/Node-js-Event-Emitter-11-320.jpg)
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");