immer-and-weakref-failed.ts

import produce, { current } from "immer";

type Node = {
  value: string;
  children: Node[];
};

const tree: Node = {
  value: "root",
  children: [
    {
      value: "a",
      children: [],
    },
    {
      value: "b",
      children: [],
    },
  ],
};

// meta
type TouchedNode = Node & { [key: string]: string };
type IndexedRoot = {
  root: TouchedNode;
  indexer: { [key: string]: any };
};

let n = 1;
const uniqueId = () => (n++).toString();
function createIndex(root: Node): IndexedRoot {
  const indexer: { [key: string]: any } = {};
  function walk(node: Node) {
    const id = uniqueId();
    (node as TouchedNode).__id__ = id;
    // @ts-ignore
    const ref = new WeakRef(node);
    indexer[id] = ref;
    node.children.forEach(walk);
  }
  walk(root);
  return {
    root: root as TouchedNode,
    indexer,
  };
}

const indexed: IndexedRoot = createIndex(tree);
const newData = produce(indexed, (draft: IndexedRoot) => {
  const ref = draft.indexer["3"]; // change b
  const target = ref.deref();
  target.value = "b-touched";
});

console.log("original", indexed);
console.log("touched", newData);

/* Result

original {
  root: {
    value: "root",
    children: [
      { value: "a", children: [Array], __id__: "2" },
      { value: "b-touched", children: [Array], __id__: "3" }
    ],
    __id__: "1"
  },
  indexer: { "1": WeakRef {}, "2": WeakRef {}, "3": WeakRef {} }
}
touched {
  root: {
    value: "root",
    children: [
      { value: "a", children: [Array], __id__: "2" },
      { value: "b-touched", children: [Array], __id__: "3" }
    ],
    __id__: "1"
  },
  indexer: { "1": WeakRef {}, "2": WeakRef {}, "3": WeakRef {} }
}
*/