makeSimpleAutoObservable.ts

makeSimpleAutoObservable.ts

import { $mobx, isObservable, makeObservable } from "mobx";

const annotationsSymbol = Symbol("annotationsSymbol");
const objectPrototype = Object.prototype;

/**
 * A purposefully-limited version of `makeAutoObservable` that supports subclasses.
 *
 * There is valid complexity in supporting `makeAutoObservable` across disparate/edge-casey
 * class hierarchies, and so mobx doesn't support it out of the box. See:
 * https://github.com/mobxjs/mobx/discussions/2850#discussioncomment-1203102
 *
 * So this implementation adds a few limitations that lets us get away with it. Specifically:
 *
 * - We always auto-infer a key's action/computed/observable, and don't support user-provided config values
 * - Subclasses should not override parent class methods (although this might? work)
 * - Only the "most child" subclass should call `makeSimpleAutoObservable`, to avoid each constructor in
 *   the inheritance chain potentially re-decorating keys.
 *
 * See https://github.com/mobxjs/mobx/discussions/2850
 */
export function makeSimpleAutoObservable(target: any): void {
  // These could be params but we hard-code them
  const overrides = {} as any;
  const options = {};

  // Make sure nobody called makeObservable/etc. previously (eg in parent constructor)
  if (isObservable(target)) {
    throw new Error("Target must not be observable");
  }

  let annotations = target[annotationsSymbol];
  if (!annotations) {
    annotations = {};
    let current = target;
    while (current && current !== objectPrototype) {
      Reflect.ownKeys(current).forEach((key) => {
        if (key === $mobx || key === "constructor") return;
        annotations[key] = !overrides ? true : key in overrides ? overrides[key] : true;
      });
      current = Object.getPrototypeOf(current);
    }
    // Cache if class
    const proto = Object.getPrototypeOf(target);
    if (proto && proto !== objectPrototype) {
      Object.defineProperty(proto, annotationsSymbol, { value: annotations });
    }
  }

  return makeObservable(target, annotations, options);
}