Experiments with JavaScript

“If you don’t like ‘this’, try Zet.js” (c) M.Nemisj

Plot: This article is about an experiment of avoiding “this” and “new” keywords in JavaScript and about the results of it.

Harmful “new” keyword and replacement for that

There are different debates flying around the internet about the safety of using “new” keyword in JavaScript. It’s all started when Douglas Crockford stated that “new” keyword can be harmful and that he doesn’t use it any more in his code. In replacement for that Douglas Crockford proposed factory functions. In public they also called sometimes Function OOP or Module pattern.

I really like dynamic nature of JavaScript, so this solution excited me. The fact that in JavaScript there is always something new to found or new to learn brings me esteem to the JavaScript language.

The only thing which I considered to be not elegant in this solution, was the inheritance paradigm. It gave me the feeling that code is too “custom”, too “hardcoded”. To fully understand what I mean, you should see it yourself:

This is how normal factory function looks like :

var User = function(){
    var privatMethod = function(){
        alert('hello');
    }

    return {
        sayHello : function(){
            privateMethod();
            this.done = true;
        }
    }
}

In the code above we created declaration of the User class. Creation of the new User instance is possible without “new” keyword:

var user1 = User();
var user2 = User();

var SubUser = function(){
    var user = User();
    var oldMethod = user.sayHello;

    user.sayHello = function(){
        oldMethod.apply(user, arguments);
        user.done = false;
    }

    return user;
}

As you can see, the declaration of subclass differs from its super-class. In my opinion this makes code less readable, and more fragile. Moreover there is too much logic involved inside the declaration of the class itself( like “apply” logic or keeping track of instance scope), so code does not become self-expressing to the reader.

That’s why my idea was to make library which would make some unified structure for Class declaration in Functional OOP style with inheritance support. There are some libraries which support Functional OOP style, but all of them, which I’ve seen are using “new” keyword. Then I’ve started with experiments and ended up with the library which is full of experiments or simply Zet.js. About all of the interesting points and experiments you can read bellow in this post.

First seeing, then believing

Before reading all this text bellow, I guess it can be interesting to see how class declaration with Zet.js looks like. Let’s redeclare SubUser :

Zet.declare('SubUser', {
    superclass : User,
    defineBody : function(that){
        Zet.public({
            sayHello : function(){
                that.inherited(arguments);
                that.done = false;
            }
        });
    }
});

Scope substitution & why no “this” usage.

Working with different people, reading articles on the net, brings me to the idea, that “this” keyword is one of the most complex concepts in the JavaScript. Especially when new developers find out that “this” can point to different scopes. Such instability of “this” keyword brings a lot of confusion, especially to the people, who came from static languages like Java or C#. First and most valuable aspect of Zet.js is, that it provides a solution to stop dealing with cumbersome “this” variable.

There are different ways in which “this” variable can be substituted. I think, it’s essential to know global/important cases, when it can occur. People, who are not interested in causalities can skip this chapter and start reading about implementation details.

As I told, by knowing most used cases it’s much more easier to identify the generic solution. One of the most important cases in my list is accessing of “this” variable from within anonymous function. Let’s look at standard non working example bellow.

User.prototype.delayMe = function(){
    setTimeout(function(){
        this.someFunction();
    },100);
}

User.prototype.delayMe = function(){
    var someFunction = this.someFunction;
    setTimeout(function(){
        someFunction();
    },100);
}

To help JavaScript developers, most frameworks and libraries offers helping functions, like “bind” (in jQuery) or “hitch” (in Dojo) to use. They help to keep correct scope at the moment of the execution.

User.prototype.delayMe = function(){
   var someFunction = dojo.hitch(this,'someFunction');
    setTimeout(function(){
        someFunction();
    },100);
}

1. Instantiate class without “new” keyword.
2. Using apply or call API calls

I will not explain first one, since the Functional OOP prevents this kind of bugs by default, but let’s check the second one.

Intentionally substitute scope can be done through call or apply API calls. By using one of this it’s possible to make “this” aim at any JavaScript object. In some situations this can be useful (hitch and bind are based on this), but also it can lead to unpredictable results.

After all this theory material it’s time to see what Zet.js proposes.

Protecting “this” with “that”

To protect “this” variable from pointing it to some-where-we-do-not-know, Zet.js prevents usage of it. Instead Zet.js forces developers to use “that” variable. This variable is available from the begin of the instance life-cycle and always points to the correct scope.

Mature JavaScript developers knows, that “this” variable can be assigned to anything(caching it). Zet.js passes “that” to the factory function at the moment of execution and it stays in the private scope of the instance. Because private scope is always available to the body of the instance, developer always have the correct value of “this” in hands.

I also want to notice that, by having such manner of declaring classes, all the private functions inside the class also automatically have the scope to the object instance. This means, that there is no more need in doing extra work like privateFunction.call(this); to access public variables or functions from the private scope.

Let’s look at the example above one more time.

Zet.declare('SubUser', {
    superclass : User,
    defineBody : function(that){
        Zet.public({
            sayHello : function(){
                that.inherited(arguments);
                that.done = false;
            }
        });
    }
});

Strange Zet.public function

I guess you’ve already noticed strange Zet.public declaration in defineBody factory. This is another experiment of mine. It is not usual to see such way of declaring things, but it is made to create logical split between functions, which are included for private purpose and public functions. Further it brings totally no functionality into the object, pure for experiment.

In case you think, this is REALLY useless, Zet.js supports also return statement as normal Functional OOP declaration does.

Zet.declare('SubUser', {
    superclass : User,
    defineBody : function(that){
        return {
            sayHello : function(){
                that.inherited(arguments);
                that.done = false;
        };
    }
});

Zet.declare('SubUser', {
    superclass : User,
    defineBody : function(that){
        that.sayHello = function(){
            that.inherited(arguments);
            that.done = false;
        }
    }
});

Functional OOP/Module pattern pitfall.

One of the strong arguments for people not to use Functional OOP is the fact that the instanceof functionality is not working correctly. Because factory function creates every time unique object instanceof will always return false. I’ve seen some solutions to fix this, but they remain using “new” keyword internally in the declarator itself. As I told already before, Zet.js is truly “new”less, so I could not use any of the solutions which I’ve seen.

Instead Zet.js extend every instance of the object with own instanceOf possibility. Passing class constructor to this function will return false/true depending if the constructor belongs to this object or to its superclass. Thus, expressions bellow will return true.

subUser1.instanceOf(User);
subUser1.instanceOf(SubUser);

// Zet instances:
Zet(User).instanceOf(User) //return true;
Zet(subUser1).instanceOf(User) //return true;


// normal instance
Zet([]).instanceOf(Array) // return true;

// String instanceof fix
"some-string" instanceof String //return false
Zet("some-string").instanceOf(String); // return true

Is there something normal in Zet.js?

Yes, besides strange .public syntax, forced “that” usage and other experimental stuff, Zet.js also has some “normal” facilities, like :

• Support for Inheritance
• Separate “initialize” call
• Declaring classes through Namespaces
• Simple loggin facilities
• Inner constructor function
• CommonJS Modules API support

This article is big enough, so I will not describe here in details  all of the listed things. If you are interested you can find all the explanation inside README file on github.

Update : As noted by Tim Caswell it’s better to name your factory functions with a “new” prefix to indicate that such constructor should be called without new keyword, for example : var person = newPerson(); Also it’s important to understand that each instance of such factory has a big impact on the memory, since it consists of own copy of all the functions of the class.

Zet.log("That's all");