How empty function "function(){}" works in JS object constructor?

Question

I am studying prototypes, classes and modular patterns with Alex MacCaw's Javascript Web Applications. Almost everything is clear and well-explained, however, I can't figure out how empty functions that are used for initialization work. I would be grateful if your explain nuances no matter how complex they are.

Here is the example from the book:

 (function($){
    var mod = {};
    mod.create = function(includes){
        var result = function(){
            this.init.apply(this, arguments);
        };
        result.fn = result.prototype;
        result.fn.init = function(){};
        result.proxy = function(func){ return $.proxy(func, this); };
        result.fn.proxy = result.proxy;
        result.include = function(ob){ $.extend(this.fn, ob); };
        result.extend = function(ob){ $.extend(this, ob); };
        if (includes) result.include(includes)
        return result;
    };
    exports.Controller = mod;
})(jQuery);

From the code above I understand that the Immediately Invoked Function Expression (IIFE) is used to protect the scope. Then mod.create construction function is defined that returns result object with all class methods. However, I am confused with how the following works:

     this.init.apply(this, arguments);
 result.fn.init = function(){};

I guess that we apply empty init function to constructor arguments to allow new objects instantiation or something like that. From the answer below it appears that init function receives undefined number of arguments, but what arguments? Those that are used during instantiation -- includes in the above code? And why this function is empty, what it does when invoked?

zerkms · Accepted Answer · 2014-06-17 10:58:56Z

1

this.init.apply(this, arguments);

is basically just

this.init(arguments[0], arguments[1], ..., arguments[N]);

But as soon as we don't know the exact number of arguments - we just use .apply()

Usage example:

var newConstructor = exports.Controller.create();
newConstructor.include({
    init: function(a, b, c) { console.log(a, b, c, 'yay!'); }
});

var newInstance = new newConstructor(1, 2, 3);

Complete demo: http://jsfiddle.net/nbq6d/1/

edited Jun 17, 2014 at 10:58

answered Jun 17, 2014 at 10:41

zerkms

256k73 gold badges447 silver badges551 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

user3695711 Over a year ago

Ok, I understand that it works on arguments array.. So it receives undefined number of arguments, but what arguments? Those that are used during instantiation -- includes in the above code? And why this function is empty, what it does when invoked?

zerkms Over a year ago

@user3695711: they are the arguments passed to a result constructor

user3695711 Over a year ago

Thanks, but still I would like to understand inner workings of this concept. So init function receives argument passed to result constructor. We get init(arg1,arg2....). How it processes them if it's empty - init: function(){}?

zerkms Over a year ago

@user3695711: added sample example on how it could be used according the code you provided

zerkms Over a year ago

@Grundy: in this case it's likely an empty function was used as a default implementation that might be overriden using .include()

|

Collectives™ on Stack Overflow

How empty function "function(){}" works in JS object constructor?

1 Answer 1

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related