Nullish coalescing and Map condition hash

snippet.js

/**
 * Just an example to showcase some conditional logic
 * 
 * Nullish coalescing operator (??) 
 *   - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing
 * Nullish coalescing assignment (??=)
 *   - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_assignment
 * Map object (new Map())
 *   - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
 * Map.getter (Map.get())
 *   - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/get
 */

const obj = {
  v: [1, 2, 3],
  w: undefined,
  x: "foo",
  y: null,
  z: 0,
};

const pxy = new Proxy(obj, {
  get(to, key) {
    return (
      Object.defineProperty(to, key, {
        value:
          new Map([
            [0, "sold out"],
            [null, "backorder"],
            [undefined, "review"],
          ]).get(to[key] ??= Reflect.get(...arguments)) ?? to?.[key],
        writable: true,
      }) ?? to
    );
  },
});

/** pxy -> {
  v: [1, 2, 3],
  w: "review"
  x: "foo"
  y: "backorder"
  z: "sold out"
} */