javascript "class" variable undefined

Question

Here: http://www.phpied.com/3-ways-to-define-a-javascript-class/ are described 3 ways to define a "class" in javascript. I chose in my code to use the 3rd method:

var apple = new function(){
    //code here
}

I use this construction as a way to separate code in namespaces, I mean I have more variable as apple in the same js file, and each one may contain functions with the same name.

var customer = new function(){
    this.URL = "//customer/";
    this.json = {};
    this.getData = function(id){
        this.prepareForm();
        this.json = requestData(this.URL);  //requestData deffined in another place
    }
    this.save = function(){
        //code
    }
    this.validate = function(){
        //code
    }
    this.prepareForm = function(){
        //code
    }
    // more code here
}


var employee = new function(){
    //code here, something like the customer code
}


var partner = new function(){
    //code here, something like the customer code
}

Now, I noticed that sometimes this.URL is undefined. The this.prepareForm() function exists, is deffined and runs on context, the variable doesn't exist and I need to call it customer.URL instead. But this is only sometimes, not all the time, and I didn't understand why and when happened.

Any suggestion? Why this happens?

If you're passing that "prepareForm" function as something like an event handler, it loses its relationship to the object. — Pointy
– Pointy, Commented Jan 23, 2014 at 16:22
this.validate(){ doesn't look right? Did you mean this.validate = function() { ? — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 23, 2014 at 16:23
Also note that that blog post is really old by JavaScript best-practice standards. — Pointy
– Pointy, Commented Jan 23, 2014 at 16:23
Edited. I wrote the cod directly on stackoverflow and I didn't saw that I didn't define well the functions. The point is that the functions are ok, my issue is with the URL variable, witch sometimes is undefined and I don't understand why! — Zelter Ady
– Zelter Ady, Commented Jan 23, 2014 at 16:39
Pointy: do you have any recommendation for a newer article about this? — Zelter Ady
– Zelter Ady, Commented Jan 23, 2014 at 16:59

Mehran Hatami · Accepted Answer · 2014-01-23 17:07:24Z

You have some syntax errors in your code and as @Pointy has pointed out, the article is really old-fashioned. I really think you have to change the way you create Javascript classes, you better use prototype to define your class methods, this is ,IMHO, the better way to do what you want:

var Customer = function Customer(){
    this.URL = "//customer/";
    this.json = {};
};
Customer.prototype.getData = function(id){
    this.prepareForm();
    this.josn = requestData(this.URL);
};
Customer.prototype.save = function()(){
    //code
};
Customer.prototype.validate = function()(){
    //code
};
Customer.prototype.prepareForm = function()(){
    //code
};
var customer = new Customer();
//you can here call your methods like:
customer.validate();

And about your specific problem regarding this.URL being undefined, this problem happens only if you call the function with a different context, it even can be passing it as a callback or handler, based on your codes I guess you are passing the getData function as an callback to a ajax call, if it is so you better create an anonymous function and call the customer.getData() in it.

ncubica · Accepted Answer · 2014-01-23 16:27:03Z

0

this.json and this.josn = requestData(this.URL) are different. cannot be the answer but surely is not the same variable. take a look.

this.json = {};
this.getData = function(id){
    this.prepareForm();
    this.josn = requestData(this.URL);  //requestData deffined in another place

answered Jan 23, 2014 at 16:27

ncubica

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3 Comments

Zelter Ady Over a year ago

Why not? I don't understand

ncubica Over a year ago

is misspelled look it one is this.json and the other this.JOSN

Zelter Ady Over a year ago

just a speling error, because I wrote all the code directly on the browser window. the real code is correct and still sometimes that variable is undefined

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