How to have a JavaScript object effectively reference itself

Question

I am trying to create some objects to store information on how to map an incoming object (from json) to a specific representation, and I use code that looks something like the following:

LocationMap = {
    fields: {
        "name": ValueMap(),
        //"parentLocation": ModelMap(LocationMap),
    }
}

PersonMap = {
    fields: {
        "name": ValueMap(),
        "location": ModelMap(LocationMap),
    }
}

The MapValue and MapModel functions can be thought of as returning functions which act on the incoming value to map it to a new value.

The trouble I'm having is with the commented out line, where I need the Location object to recursively reference itself, which is of course impossible. If these were classes in another language I think there could be a recursive reference. How can I accomplish the same thing with JavaScript?

I made a small working example on jsfiddle.

`obj = {...}; obj.fields.location = ModelMap(obj);` perhaps? — Niet the Dark Absol, Aug 17 '18 at 11:26
@NiettheDarkAbsol you are right, after fixing some typos, that works — user3885964, Aug 17 '18 at 11:38

slebetman · Accepted Answer · 2018-08-17T12:21:06.880

0

If these were classes in another language I think there could be a recursive reference

These are objects, not classes. The problem you are having is you are not used to anonymous classes or object literals. The solution is simple, make them classes:

class LocationMap {
  constructor () {
    this.fields = {
      name: valueMap(),
      location: modelMap(this)
    };
  }
}

class PersonMap = {
  constructor () {
    this.fields = {
      name: valueMap(),
      location: modelMap(locationMap)
    };
  }
}

var locationMap = new LocationMap();
var personMap = new PersonMap();

if you're running in an environment that doesn't support ES6 syntax then you can use the old-school syntax:

function LocationMap () {
  this.fields = {
    name: valueMap(),
    location: modelMap(this)
  };
}

function PersonMap () {
  this.fields = {
    name: valueMap(),
    location: modelMap(locationMap)
  };
}

var locationMap = new LocationMap();
var personMap = new PersonMap();

You can also manually construct the objects:

var locationMap = {};
locationMap.fields = {};
locationMap.fields.name = valueMap();
locationMap.fields.location = modelMap(locationMap);

var personMap = {};
locationMap.fields = {};
locationMap.fields.name = valueMap();
locationMap.fields.location = modelMap(locationMap);

edited Aug 17 '18 at 12:21

answered Aug 17 '18 at 11:29

slebetman

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I don't understand your use of locationMap(this) in your examples – user3885964 Aug 17 '18 at 11:49
You said you want to pass the object itself back into locationMap - that's what I'm doing – slebetman Aug 17 '18 at 12:19
Wait.. OK. That's not what you're doing for personMap. Let me edit the code – slebetman Aug 17 '18 at 12:20
@slebetman If it can have multiple instances (otherwise you shouldn't make it a `class`) you probably want to make `locationMap` a parameter of the `PersonMap` constructor – Bergi Aug 17 '18 at 12:49
Thanks @slebetman I see that I probably could have found more info about this if I had done some more searching – user3885964 Aug 17 '18 at 15:40

How to have a JavaScript object effectively reference itself

1 Answers1