Create model relationships with mobx

modeled-mobx is a lightweight layer on top of MobX 6 to easily serialize and hydrate javascript classes to/from JSON

Introduction

modeled-mobx replaces mobx's makeObservable with a modelize function. modelize adds "field" and "model" properties to configure the model's fields as observables that get and set their values when serialize and hydrate respectively are called.

It also includes a field and model decorator that can optionally be used instead of specifiying each property on the options passed to modelize

Example

import { modelize, field, model, hydrateModel, serialize, getParentOf } from 'modeled-mobx'
import { observable, computed } from 'mobx'

class Item {
    name = '' 
    material = ''
    get box() { return getParentOf<Box>(this) }
    constructor() {
        modelize(this, {
            name: field,
            material: observable,
        })
    }
}

// an example using decorators
export class Box {

    @field width = 0;
    @field height = 0;
    @field depth = 0;

    @observable serial: number = 0; // observable from mobx will be set by hydrate
                                    // and initialized by modelize.  It will not be serialized
    @computed get volume() {
        return this.width * this.height * this.depth;
    }

    @model(Item) items: Item[] = []; // note: this is an array of "item" models
    @model(Item) defaultItem?: Item; // and this one is a single model

    constructor() {
        modelize(this) // individual fields do not need to be specified when using decorators
    }
}


const box = hydrateModel(Box, {
    width: 10, height: 10, depth: 10, serial: 1234,
    items: [{ name: 'Box #1' }, { name: 'Box #2' }],
    defaultItem: { name: 'Fruit' },
})

console.log(box.items[1].name, box.volume) // Box #2, 1000
console.log(box.items[1].box === box) // true 
console.log(serialize(box))
// {
//   width: 10, height: 10, depth: 10,
//   items: [{ name: 'Box #1' }, { name: 'Box #2' }],
//    defaultItem: { name: 'Fruit' }
//  }

Edge cases and limitations

properties must be assigned a value

When using Javascript decorators and uninitialized properties, Mobx may raise an exception: Cannot apply 'observable' to '<property name>': Field not found. This is caused by an incorrect babel configuration. More info: #1

there must be properties to decorate

An exception will be raised if modelize is called with no properties and none are decorated.

class EmptyThing {
   name = 'empty'
   constructor() {
      modelize(this);
   }
}

new EmptyThing() // raises "[MobX] No annotations were passed to makeObservable, but no decorated members have been found either"

inheritance is tricky

There have been multiple bugs worked around in attempting to inherit from a modelized base class. It now seems to be working but there may still be lingering bugs. Please open issues if you note any weirdness.