In the realm of JavaScript, "this" is a key player when referring to an object within a factory

I created some JavaScript classes and FunctionFactories for them, but I believe there are errors in my implementation.

To make the code more understandable, I decided to rename certain parts of it.

The main class is called the "root"-class, which has children that are added later on.

function templateRoot(){
    this.id = "root";
    this.parent = null;
    this.children = [];

    this.editable = true; // bla

    this.render = function(){
        $.each(this.children,function(i,obj){
            this.children[i].render();
            var baseButtons = this.getBaseButtons();
            $('#'+this.id).append(baseButtons);
        });
    };
    this.addBase = addBaseFactory(this);
};

The "addBase" attribute receives a function from the addBaseFactory...

function addBaseFactory(that){
    return function(){
        var newBase = new base(that.children.length, that.id);
        that.children.push(newBase);
    };
}

...and here is the base class used to generate an object in the "addBase" method:

function base(count, parent){
    this.id = parent+"_base"+count;
    this.parent = parent;
    this.children = [];
    this.remove = function (){
        $('#'+this.id).remove();        
    };
    this.render = baseRenderFactory(this);
    this.addChild = addChildFactory(this);
    this.getBaseButtons = function(){
        var addAttributeButton = new $("<button>+ Attribute</button>").button();
        var addTextButton = new $("<button>+ Text</button>").button();
        return [addAttributeButton, addTextButton];
    };
}

The issue arises when debugging the code and setting a breakpoint within the "render" function of the root-object. At this point, "this" refers to the "base" object instead of the "root" object. This confuses me because the "root" object should be the owner of this function, and the base has its own render function which is not directly called there.

Even in the line:

$.each(this.children,function(i,obj){

"this" points to the "base" object while it should be referring to the "root" object.

I hope someone can assist me with this :-)


EDIT:

The code to execute it:

var test = new templateRoot();
test.addBase();
test.render();

EDIT 2:

In the "addBaseFactory," "that" correctly references the "base" object.

Answer №1

Your explanation seems a bit confusing, so I may have misunderstood your intentions. It appears that you are expecting the this keyword within your nested functions to refer to the same object as in the outer templateRoot() function. However, it's important to note that in JavaScript, each function has its own unique this object and nested functions do not inherit from the containing function.

An alternative solution is to utilize the concept that nested functions can access variables from their parent functions. Here is an example implementation:

function templateRoot(){
    var self = this; // save a reference to this for use in nested functions
    this.id = "root";
    this.parent = null;
    this.children = [];

    this.editable = true;

    this.render = function(){
        $.each(self.children,function(i,obj){
            self.children[i].render();
            var baseButtons = this.getBaseButtons();
            $('#'+self.id).append(baseButtons);
        });
    };
    this.addBase = addBaseFactory(this);
};

To gain a deeper understanding of how the this keyword works in JavaScript, you can visit MDN.

Answer №2

Is it possible that this will display the children of its children, as jQuery sends each child individually?

this.display = function(){
    $.each(this.children,function(i,obj){
        this.children[i].display();
        var baseButtons = this.getBaseButtons();
        $('#'+this.id).append(baseButtons);
    });
};

By the way, in which context is addBaseFactory invoked? I am concerned that the "this" in the base might point to that particular scope.

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