Resonate TypeScript SDK

About this component

The Resonate TypeScript SDK enables developers to build reliable and scalable cloud applications across a wide variety of use cases.

• How to contribute to this SDK
• Evaluate Resonate for your next project
• Example application library
• Distributed Async Await — the concepts that power Resonate
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Quickstart

1. Install the Resonate Server & CLI

brew install resonatehq/tap/resonate

2. Install the Resonate SDK

npm install @resonatehq/sdk

3. Write your first Resonate Function

A countdown as a loop. Simple, but the function can run for minutes, hours, or days, despite restarts.

import { Resonate, type Context } from "@resonatehq/sdk";

function* countdown(context: Context, count: number, delay: number) {
  for (let i = count; i > 0; i--) {
    // Run a function, persist its result
    yield* context.run((context: Context) => console.log(`Countdown: ${i}`));
    // Sleep
    yield* context.sleep(delay * 1000);
  }
  console.log("Done!");
}
// Instantiate Resonate
const resonate = new Resonate({ url: "http://localhost:8001" });
// Register the function
resonate.register(countdown);

Clone a working example repo

4. Start the server

resonate dev

5. Start the worker

npx ts-node countdown.ts

6. Run the function

Run the function with execution ID countdown.1:

resonate invoke countdown.1 --func countdown --arg 5 --arg 60

Result

You will see the countdown in the terminal

npx ts-node countdown.ts
Countdown: 5
Countdown: 4
Countdown: 3
Countdown: 2
Countdown: 1
Done!

What to try

After starting the function, inspect the current state of the execution using the resonate tree command. The tree command visualizes the call graph of the function execution as a graph of durable promises.

resonate tree countdown.1

Now try killing the worker mid-countdown and restarting. The countdown picks up right where it left off without missing a beat.

Async/await

The SDK also ships an async/await engine: the same durable model, written with ordinary async functions instead of generators. Import it from @resonatehq/sdk/async:

import { Resonate, type Context } from "@resonatehq/sdk/async";

async function countdown(ctx: Context, count: number, delay: number) {
  for (let i = count; i > 0; i--) {
    // Run a function, persist its result
    await ctx.run((ctx: Context) => console.log(`Countdown: ${i}`));
    // Sleep
    await ctx.sleep(delay * 1000);
  }
  console.log("Done!");
}

// Instantiate Resonate
const resonate = new Resonate({ url: "http://localhost:8001" });
// Register the function
resonate.register(countdown);

Same server, same CLI, same durable promises — the rest of the quickstart is unchanged.

One difference to know about: operations are eager. Calling ctx.run(...) starts the work immediately and returns an awaitable handle, so fan-out is ordinary promise code:

async function checkout(ctx: Context) {
  const payment = ctx.run(chargeCard);     // starts now
  const inventory = ctx.run(reserveItems); // runs concurrently
  return await Promise.all([payment, inventory]);
}

Migrating from generators

Both engines live in the same package and speak the same protocol to the same server, so you can migrate one function at a time. The mechanical changes:

Generator engine	Async engine
import { Resonate } from "@resonatehq/sdk"	import { Resonate } from "@resonatehq/sdk/async"
function* (context: Context, ...)	async function (ctx: Context, ...)
yield* context.run(...), yield* context.sleep(...)	await ctx.run(...), await ctx.sleep(...)
yield context.beginRun(...), later yield future	const p = ctx.run(...), later await p — every op is eager
resonate.run(id, func, ...args) → the result	resonate.run(id, func, ...args) → a handle; await handle.result()
resonate.beginRun(id, func, ...args) → a handle	same call — there are no begin* variants, run is begin-run

Two things to watch:

• Retries are opt-in. The generator engine retries plain functions with exponential backoff by default. The async engine never retries by default — an async workflow and a plain async function are indistinguishable at runtime, so there is no safe blanket default. To keep retry behavior, pass a policy explicitly:

  import { Exponential } from "@resonatehq/sdk/async";
  
  await ctx.run(chargeCard, ctx.options({ retryPolicy: new Exponential() }));

• Only await durable promises inside a workflow. A plain await on a timer or network call is invisible to the engine — the workflow may resume after its execution pass has ended and abort. Wrap side effects in ctx.run, the same rule as context.run in the generator engine.