Javascript Object Inheritance how to get the Child instance name

Question

/**
 * adds an entry to the list
 * 
 * @param data {Object}
 * @return this
 */
ElementList.prototype.addEntry = function(data){
    if (!data) return this;

    data['type'] = this.children_type;

    // add the entry to the current elements
    this.element_list.push(new FavoriteEntry(data));

    this.refresh();

    return this;
};

/**
 * favorites extend ElementList
 *
 * @param setting_list
 * @constructor
 */
function FavoriteList(setting_list){
    ElementList.call(this, setting_list);
}

FavoriteList.prototype = new ElementList();
FavoriteList.constructor = FavoriteList;

So this a short code snipplet of an educational project of mine. What I want to do is reduce repeating code so I created a generic ElementList object So

the Example FavoriteList inherties the parent Objects prototype
The constructors is pointing to the Childobject
the Parent constructor is called within the child.

That works just perfectly fine my problem is

 // add the entry to the current elements
this.element_list.push(new FavoriteEntry(data));

This should create a new instance of an Object BASED on the CHILD so therefore I need to get the name of the child instance that's calling the parent method

i tried - this.constructor (point to the parent) - this.constructor.name - this instanceof FavoriteList (works)

since I DON'T want to pass a name and i think iterating through instanceof "options" is not really smart.

I would ask for some insights how I can access the childs instance name in the parent elements method body.

Please I only need an explicit answer to this!! I already read workarounds! If It's not possible just say so :)

thx in advance :)

I'm confused: So you do something like this: `var favList = new FavoriteList("xyz"); favList.addEntry("some data");` and you want to access `favList` inside of `addEntry`? — basilikum, Jan 14 '14 at 14:11
well the data is an object not a string -> it creates element in predefined html container. but since the events should be handled different base on the parent container i need to create dynamic instances of the "entries" the FavList should contain FavEntries so I want to generate the "FavEntries" call -> "var call = FavList.constructor.replace(/List/, '')" + "Entry"(); something like that. — shadowdroid, Jan 14 '14 at 14:37
var call = this.constructor.name.replace('List','') + "Entry"; window[call](data); that's what i wanted to do to be excact :) — shadowdroid, Jan 14 '14 at 14:43

score 1 · Answer 1 · edited May 23 '17 at 10:27

this.element_list.push(new FavoriteEntry(data));
This should create a new instance of an Object BASED on the CHILD so therefore I need to get the name of the child instance that's calling the parent method

No, you don't seem to need to know the name. All you need is a helper function to generate new Entry instances, that can be overwritten to generate more specific entries. Maybe you're already doing that by passing a children_type with the data…

i tried - this.constructor (point to the parent)

It should work if you had set the constructor correctly. Change your code to

FavoriteList.prototype.constructor = FavoriteList;
//          ^^^^^^^^^^

Also, you might want to use Object.create instead of new to set up the prototype chain.

ahh okay that made sense :) works like a charm now. i already change it to the ecma standard Object.create I just didn't want to repost the code :) thx for the input :) — shadowdroid, Jan 14 '14 at 14:32

score 1 · Answer 2 · answered Jan 14 '14 at 15:37

I'm not sure if I fully understand but the code new FaforiteEntry should create either a FororiteEntry or another type based on the current object type.

Maybe the following example could help you out:

var ElementList = function(args) {
  this.element_list = [];
}
ElementList.prototype.addEntry = function(args) {
  this.element_list.push(new this.entryType(args.val));
};
//will create element_list items of type String
ElementList.prototype.entryType = String;

function FavoriteList(args) {
  ElementList.call(this, args);
}
FavoriteList.prototype = Object.create(ElementList.prototype);
FavoriteList.constructor = FavoriteList;
//will create element_list items of type Array
FavoriteList.prototype.entryType = Array;

//adding entries to f would create items of type Array
var f = new FavoriteList();
f.addEntry({val: 2});
console.log(f.element_list);//[[undefined, undefined]]
//adding entries to e would create items of type String
var e = new ElementList();
e.addEntry({val: 2});
console.log(e.element_list);//[ String { 0="2"...

thx but Bergi gave me the answer I needed. i had to assign the obj.prototype.constructor so I could access the name of the child object that called the generic object. :) `var call = this.constructor.name.replace('List','') + "Entry"; // add the entry to the current elements this.element_list[data.id] = new window[call](data);` that's what I wanted to do :) — shadowdroid, Jan 14 '14 at 15:55
@shadowdroid I see, please note that the variable FavoriteList is assigned to a nameless function in my code and this.name would not return what you expect. — HMR, Jan 15 '14 at 00:01

score 1 · Answer 3 · answered Apr 06 '15 at 04:30

1

Simple code example:

 function Parent(){
        // custom properties
    }

    Parent.prototype.getInstanceName = function(){
        for (var instance in window){
            if (window[instance] === this){
                return instance;
            }
        }
    };

    var child = new Parent();

    console.log(child.getInstanceName()); // outputs: "child"

answered Apr 06 '15 at 04:30

shmuli

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1

@shadowdroid Note: This implementation works if the instance was created in the root. – shmuli Apr 16 '15 at 00:08

Javascript Object Inheritance how to get the Child instance name

3 Answers3