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Immer produce with patches and inverse patches: working versions (tested 2026-10-15)

Update immutable state with Immer produce, capture patches and inversePatches for undo, and applyPatches to replay edits in tests.

passed1 passed · 0 failed2026-10-15 16:01 UTC
Status
passed
Last passed
2026-10-15 16:01 UTC
Tests
1 / 1
Language
TypeScript
Runtime
node v22.23.3
pinned versions3
immer@11.1.21@types/node@26.6.5tsx@4.23.15
run it
npm install --no-audit --no-fund --ignore-scripts=false
npm test
test environment
node v22.23.3
linux 6.17.0-1022-azure
x64
runner: github-actions 38764699834

The code

Exactly the files that passed. Your agent can pull them with get_recipe("immer-patches-history") (install), or see them on GitHub.

package.json
{
  "name": "immer-patches-history",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "immer": "11.1.21"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}
src/store.ts
import { applyPatches, enablePatches, produceWithPatches, type Patch } from "immer";

enablePatches();

export type Todo = { id: number; text: string; done: boolean };
export type State = { todos: Todo[]; nextId: number };

export function createState(): State {
  return { todos: [], nextId: 1 };
}

export function addTodo(state: State, text: string) {
  return produceWithPatches(state, (draft) => {
    draft.todos.push({ id: draft.nextId++, text, done: false });
  });
}

export function toggleTodo(state: State, id: number) {
  return produceWithPatches(state, (draft) => {
    const t = draft.todos.find((x) => x.id === id);
    if (t) t.done = !t.done;
  });
}

export function undo(state: State, inverse: Patch[]) {
  return applyPatches(state, inverse);
}

export function redo(state: State, patches: Patch[]) {
  return applyPatches(state, patches);
}
test/store.test.ts
import { test } from "node:test";
import assert from "node:assert/strict";
import { addTodo, createState, redo, toggleTodo, undo } from "../src/store.ts";

test("produceWithPatches supports undo and redo", () => {
  let state = createState();
  const [s1, patches, inverse] = addTodo(state, "write recipe");
  state = s1;
  assert.equal(state.todos.length, 1);
  assert.equal(state.todos[0].done, false);

  const [s2, p2, i2] = toggleTodo(state, 1);
  state = s2;
  assert.equal(state.todos[0].done, true);

  state = undo(state, i2);
  assert.equal(state.todos[0].done, false);
  state = redo(state, p2);
  assert.equal(state.todos[0].done, true);

  state = undo(state, inverse);
  assert.equal(state.todos.length, 0);
  state = redo(state, patches);
  assert.equal(state.todos[0].text, "write recipe");
});

Connect to ProvenPin

Add the free MCP server so your agent can pull this recipe and others like it. Same setup as the docs.

terminal
claude mcp add --transport http provenpin https://mcp.provenpin.com/mcp

Any other MCP client: Streamable HTTP at https://mcp.provenpin.com/mcp. No API key, no signup.