Defining a jQuery ajax callback parameter as an existing object type

Question

I admit this question is getting to the limits of what I know of JavaScript & jQuery, and there is probably a more proper way to state my question (which would help in finding an existing solution), but if you can bear with me, this is what I'm after.

I have an existing object class I've defined. I'm making a jQuery ajax call using getJSON, and I want my callback parameter (which is an object) to be classed as my custom object, so that I can access that class' methods from it.

So I have some object class

function Boo() {

  this.param1;
  this.param2;

  this.yah = function() {
     ...
  }

}

and then I have something elsewhere of the sort

$.getJSON(url,function(new_instance) {
   //from my php source this passed object is already loaded with param1, param2...
   alert(new_instance.param1);    //no probs
   //but i want to be able to then call
   new_instance.yah();
});

In other words, I want new_instance to be considered an instance of Boo(). I know in stuff like ActionScript you have to class the incoming parameters for exactly this reason, dunno what flexibility I have in JS.

I thought maybe about having an intermediate function that takes in the incoming object and creates/populates a new instance of Boo() but not sure if there is a more clever method.

Many thanks!!

To both responses so far, yes I know I should be prototyping (;D), you may assume that my final product will be more efficiently written... — Dan
– Dan, Commented Jan 21, 2012 at 15:49

Esailija · Accepted Answer · 2012-01-21 15:38:51Z

1

Do not define methods in the constructor function, you are defining them over and over again every time the costructor is called. Move them over to the prototype:

Boo.prototype = {

    yah: function() {

    },

    bah: function() {

    }

    ...

};

a little helper function:

function coerceTo( proto, values ) {
    var r = Object.create( proto );
    for( var key in values ) {
        r[key] = values[key];
    }

    return r;
}

Depending on browser, Object.create might not be available, so:

if (!Object.create) {
    Object.create = function (o) {
        if (arguments.length > 1) {
            throw new Error('Object.create implementation only accepts the first parameter.');
        }
        function F() {}
        F.prototype = o;
        return new F();
    };
}

Usage:

new_instance = coerceTo( Boo.prototype, new_instance );

new_instance instanceof Boo //true
new_instance.yah();

answered Jan 21, 2012 at 15:38

Esailija

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1 Comment

Dan Over a year ago

Here's what I did, it isn't properly prototyped but the general idea is there... <code>Boo.prototype.dp(params,callback) { $.getJSON(params,function(r){ if (typeof(r) == 'object') { //this line i realize can be written better as above var t = new Boo(); //loop and load up params here (not shown) callback(t); } else { callback(r); } }); another_instance.dp(params,function(new_instance) { new_instance.yah(); //hooray! } );</code>

dfsq · Accepted Answer · 2012-01-21 15:44:46Z

0

What you can do:

$.getJSON(url,function(newObjData) {
   var newObj = $.extend(new Boo(), newObjData);
   newObj.yah();
});

Also consider moving your Boo methods to object prototype so the methods don't get recreated for each Boo instance:

var Boo = function() {
    this.param1;
    this.param2;
}

Boo.prototype.yah = function() {
    console.log(this.param1);
}

edited Jan 21, 2012 at 15:44

answered Jan 21, 2012 at 15:38

dfsq

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3 Comments

Esailija Over a year ago

Calling the original constructor like this can cause side effects or errors.

Dan Over a year ago

OK many thanks for both answers, this one looks ideally low-budget, granted as I'm building an API I was hoping to be extra fussy and somehow let the users just use myfunction(params,function(boo){ .. } and use 'boo' as a Boo() right away in their scripts, but probably asking too much!

dfsq Over a year ago

All depends on your needs. But I should admit that the answer of @Esailija is conceptually correct and more robust.

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