Question

I am just curious to know what is the purpose of,

function MyStream() {
    events.EventEmitter.call(this);
}

in the following block of code taken from Nodejs.org Docs section,

var util = require("util");
var events = require("events");

function MyStream() {
    events.EventEmitter.call(this);
}

util.inherits(MyStream, events.EventEmitter);

MyStream.prototype.write = function(data) {
    this.emit("data", data);
}

var stream = new MyStream();

console.log(stream instanceof events.EventEmitter); // true
console.log(MyStream.super_ === events.EventEmitter); // true

stream.on("data", function(data) {
    console.log('Received data: "' + data + '"');
})
stream.write("It works!"); // Received data: "It works!"

Please explain.

Answer 1

This isn’t the first time this question has been asked: https://groups.google.com/forum/#!topic/nodejs/ab_Xih1L5R8/discussion

Quote from Bradley Meck:

Using EventEmitter.call on an object will do the setup of instance methods / properties (not inherited) of an EventEmitter. It is similar in purpose to super(…) in Java or base(…) in C#, but it is not implicit in Javascript. Because of this, we must manually call it ourselves. As for the talk about util.inherits, this will make the MyStream function inherit from another prototyped function so that instanceof works (side note: javascript only allows single inheritance). Due to how the new operator works, if we have the this variable in a function set to an instanceof EventEmitter, and call EventEmitter.call it look for all intents and purposes as if EventEmitter’s constructor is being called on our MyStream object.