ProvenPin Install

p-defer deferred promises: working versions (tested 2026-10-16)

Create deferred promises with p-defer, settle them later from outside, and assert resolve, reject and thenable behavior offline.

passed3 passed · 0 failed2026-10-16 17:50 UTC
Status
passed
Last passed
2026-10-16 17:50 UTC
Tests
3 / 3
Language
TypeScript
Runtime
node v22.23.3
pinned versions3
p-defer@4.0.1@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 38942732901

The code

Exactly the files that passed. Your agent can pull them with get_recipe("p-defer-manual") (install), or see them on GitHub.

package.json
{
  "name": "p-defer-manual",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "p-defer": "4.0.1"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}
src/deferred.ts
import pDefer, { type DeferredPromise } from "p-defer";

export type Deferred<T> = {
  promise: Promise<T>;
  resolve: (value: T | PromiseLike<T>) => void;
  reject: (error?: unknown) => void;
};

export function createDeferred<T>(): Deferred<T> {
  const deferred: DeferredPromise<T> = pDefer<T>();
  return deferred;
}

export function isThenable(value: unknown): value is PromiseLike<unknown> {
  return (
    (typeof value === "object" || typeof value === "function") &&
    value !== null &&
    typeof (value as { then?: unknown }).then === "function"
  );
}
test/deferred.test.ts
import { test } from "node:test";
import assert from "node:assert/strict";
import { createDeferred, isThenable } from "../src/deferred.ts";

test("resolves a deferred promise from outside", async () => {
  const deferred = createDeferred<number>();
  assert.equal(isThenable(deferred.promise), true);

  const seen: number[] = [];
  const tapped = deferred.promise.then((value) => {
    seen.push(value);
    return value;
  });

  deferred.resolve(42);
  assert.equal(await tapped, 42);
  assert.deepEqual(seen, [42]);
});

test("rejects a deferred promise from outside", async () => {
  const deferred = createDeferred<number>();
  assert.equal(isThenable(deferred.promise), true);

  let caught: unknown;
  const tapped = deferred.promise.catch((error) => {
    caught = error;
  });

  const boom = new Error("boom");
  deferred.reject(boom);
  await tapped;
  assert.equal(caught, boom);
});

test("thenable check distinguishes promises from plain values", () => {
  assert.equal(isThenable({ then: 1 }), false);
  assert.equal(isThenable(null), false);
  assert.equal(isThenable(undefined), false);
  assert.equal(isThenable(Promise.resolve()), true);
});

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.