---
title: "Tasks: Overview"
sidebarTitle: "Overview"
description: "Tasks are functions that can run for a long time and provide strong resilience to failure."
---

There are different types of tasks including regular tasks and [scheduled tasks](/tasks/scheduled).

## Hello world task and how to trigger it

Here's an incredibly simple task:

```ts /trigger/hello-world.ts
import { task } from "@trigger.dev/sdk";

const helloWorld = task({
  //1. Use a unique id for each task
  id: "hello-world",
  //2. The run function is the main function of the task
  run: async (payload: { message: string }) => {
    //3. You can write code that runs for a long time here, there are no timeouts
    console.log(payload.message);
  },
});
```

You can trigger this in two ways:

1. From the dashboard [using the "Test" feature](/run-tests).
2. Trigger it from your backend code. See the [full triggering guide here](/triggering).

Here's how to trigger a single run from elsewhere in your code:

```ts Your backend code
import { helloWorld } from "./trigger/hello-world";

async function triggerHelloWorld() {
  //This triggers the task and returns a handle
  const handle = await helloWorld.trigger({ message: "Hello world!" });

  //You can use the handle to check the status of the task, cancel and retry it.
  console.log("Task is running with handle", handle.id);
}
```

You can also [trigger a task from another task](/triggering), and wait for the result.

## Defining a `task`

The task function takes an object with the following fields.

### The `id` field

This is used to identify your task so it can be triggered, managed, and you can view runs in the dashboard. This must be unique in your project – we recommend making it descriptive and unique.

### The `run` function

Your custom code inside `run()` will be executed when your task is triggered. It’s an async function that has two arguments:

1. The run payload - the data that you pass to the task when you trigger it.
2. An object with `ctx` about the run (Context), and any output from the optional `init` function that runs before every run attempt.

Anything you return from the `run` function will be the result of the task. Data you return must be JSON serializable: strings, numbers, booleans, arrays, objects, and null.

### `retry` options

A task is retried if an error is thrown, by default we retry 3 times.

You can set the number of retries and the delay between retries in the `retry` field:

```ts /trigger/retry.ts
export const taskWithRetries = task({
  id: "task-with-retries",
  retry: {
    maxAttempts: 10,
    factor: 1.8,
    minTimeoutInMs: 500,
    maxTimeoutInMs: 30_000,
    randomize: false,
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

For more information read [the retrying guide](/errors-retrying).

It's also worth mentioning that you can [retry a block of code](/errors-retrying) inside your tasks as well.

### `queue` options

Queues allow you to control the concurrency of your tasks. This allows you to have one-at-a-time execution and parallel executions. There are also more advanced techniques like having different concurrencies for different sets of your users. For more information read [the concurrency & queues guide](/queue-concurrency).

```ts /trigger/one-at-a-time.ts
export const oneAtATime = task({
  id: "one-at-a-time",
  queue: {
    concurrencyLimit: 1,
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

### `machine` options

Some tasks require more vCPUs or GBs of RAM. You can specify these requirements in the `machine` field. For more information read [the machines guide](/machines).

```ts /trigger/heavy-task.ts
export const heavyTask = task({
  id: "heavy-task",
  machine: {
    preset: "large-1x", // 4 vCPU, 8 GB RAM
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

### `maxDuration` option

By default tasks can execute indefinitely, which can be great! But you also might want to set a `maxDuration` to prevent a task from running too long. You can set the `maxDuration` on a task, and all runs of that task will be stopped if they exceed the duration.

```ts /trigger/long-task.ts
export const longTask = task({
  id: "long-task",
  maxDuration: 300, // 300 seconds or 5 minutes
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

See our [maxDuration guide](/runs/max-duration) for more information.

## Global lifecycle hooks

<Note>When specifying global lifecycle hooks, we recommend using the `init.ts` file.</Note>

You can register global lifecycle hooks that are executed for all runs, regardless of the task. While you can still define these in the `trigger.config.ts` file, you can also register them anywhere in your codebase:

```ts
import { tasks } from "@trigger.dev/sdk";

tasks.onStart(({ ctx, payload, task }) => {
  console.log("Run started", ctx.run);
});

tasks.onSuccess(({ ctx, output }) => {
  console.log("Run finished", ctx.run);
});

tasks.onFailure(({ ctx, error }) => {
  console.log("Run failed", ctx.run);
});
```

### `init.ts`

If you create a `init.ts` file at the root of your trigger directory, it will be automatically loaded when a task is executed. This is useful if you want to register global lifecycle hooks, or initialize a database connection, etc.

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onStart(({ ctx, payload, task }) => {
  console.log("Run started", ctx.run);
});
```

## Lifecycle functions

![Lifecycle functions](/images/lifecycle-functions.png)

### `middleware` and `locals` functions

Our task middleware system runs at the top level, executing before and after all lifecycle hooks. This allows you to wrap the entire task execution lifecycle with custom logic.

<Info>
  An error thrown in `middleware` is just like an uncaught error in the run function: it will
  propagate through to `catchError()` function and then will fail the attempt (either causing a
  retry or failing the run).
</Info>

The `locals` API allows you to share data between middleware and hooks.

```ts db.ts
import { locals } from "@trigger.dev/sdk";
import { logger, tasks } from "@trigger.dev/sdk";

// This would be type of your database client here
const DbLocal = locals.create<{ connect: () => Promise<void>; disconnect: () => Promise<void> }>(
  "db"
);

export function getDb() {
  return locals.getOrThrow(DbLocal);
}

export function setDb(db: { connect: () => Promise<void> }) {
  locals.set(DbLocal, db);
}

tasks.middleware("db", async ({ ctx, payload, next, task }) => {
  // This would be your database client here
  const db = locals.set(DbLocal, {
    connect: async () => {
      logger.info("Connecting to the database");
    },
    disconnect: async () => {
      logger.info("Disconnecting from the database");
    },
  });

  await db.connect();

  await next();

  await db.disconnect();
});

// Disconnect when the run is paused
tasks.onWait("db", async ({ ctx, payload, task }) => {
  const db = getDb();
  await db.disconnect();
});

// Reconnect when the run is resumed
tasks.onResume("db", async ({ ctx, payload, task }) => {
  const db = getDb();
  await db.connect();
});
```

You can access the database client using `getDb()` in your tasks `run` function and all your hooks (global or task specific):

```ts
import { getDb } from "./db";

export const myTask = task({
  run: async (payload: any, { ctx }) => {
    const db = getDb();
    await db.query("SELECT 1");
  },
});
```

### `onStartAttempt` function

<Info>The `onStartAttempt` function was introduced in v4.1.0</Info>

Before a task run attempt starts, the `onStartAttempt` function is called. It's useful for sending notifications, logging, and other side effects.

```ts /trigger/on-start.ts
export const taskWithOnStartAttempt = task({
  id: "task-with-on-start-attempt",
  onStartAttempt: async ({ payload, ctx }) => {
    //...
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

You can also define a global `onStartAttempt` function using `tasks.onStartAttempt()`.

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onStartAttempt(({ ctx, payload, task }) => {
  console.log(
    `Run ${ctx.run.id} started on task ${task} attempt ${ctx.run.attempt.number}`,
    ctx.run
  );
});
```

<Info>Errors thrown in the `onStartAttempt` function will cause the attempt to fail.</Info>

If you want to execute code before just the first attempt, you can use the `onStartAttempt` function and check `ctx.run.attempt.number === 1`:

```ts /trigger/on-start-attempt.ts
export const taskWithOnStartAttempt = task({
  id: "task-with-on-start-attempt",
  onStartAttempt: async ({ payload, ctx }) => {
    if (ctx.run.attempt.number === 1) {
      console.log("Run started on attempt 1", ctx.run);
    }
  },
});
```

### `onWait` and `onResume` functions

These lifecycle hooks allow you to run code when a run is paused or resumed because of a wait:

```ts
export const myTask = task({
  id: "my-task",
  onWait: async ({ wait }) => {
    console.log("Run paused", wait);
  },
  onResume: async ({ wait }) => {
    console.log("Run resumed", wait);
  },
  run: async (payload: any, { ctx }) => {
    console.log("Run started", ctx.run);

    await wait.for({ seconds: 10 });

    console.log("Run finished", ctx.run);
  },
});
```

You can also define global `onWait` and `onResume` functions using `tasks.onWait()` and `tasks.onResume()`:

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onWait(({ ctx, payload, wait, task }) => {
  console.log("Run paused", ctx.run, wait);
});

tasks.onResume(({ ctx, payload, wait, task }) => {
  console.log("Run resumed", ctx.run, wait);
});
```

### `onSuccess` function

When a task run succeeds, the `onSuccess` function is called. It's useful for sending notifications, logging, syncing state to your database, or other side effects.

```ts /trigger/on-success.ts
export const taskWithOnSuccess = task({
  id: "task-with-on-success",
  onSuccess: async ({ payload, output, ctx }) => {
    //...
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

You can also define a global `onSuccess` function using `tasks.onSuccess()`.

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onSuccess(({ ctx, payload, output }) => {
  console.log("Task succeeded", ctx.task.id);
});
```

<Info>
  Errors thrown in the `onSuccess` function will be ignored, but you will still be able to see them
  in the dashboard.
</Info>

### `onComplete` function

This hook is executed when a run completes, regardless of whether it succeeded or failed:

```ts /trigger/on-complete.ts
export const taskWithOnComplete = task({
  id: "task-with-on-complete",
  onComplete: async ({ payload, output, ctx }) => {
  if (result.ok) {
    console.log("Run succeeded", result.data);
  } else {
    console.log("Run failed", result.error);
  }
});
```

You can also define a global `onComplete` function using `tasks.onComplete()`.

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onComplete(({ ctx, payload, output }) => {
  console.log("Task completed", ctx.task.id);
});
```

<Info>
  Errors thrown in the `onComplete` function will be ignored, but you will still be able to see them
  in the dashboard.
</Info>

### `onFailure` function

When a task run fails, the `onFailure` function is called. It's useful for sending notifications, logging, or other side effects. It will only be executed once the task run has exhausted all its retries.

```ts /trigger/on-failure.ts
export const taskWithOnFailure = task({
  id: "task-with-on-failure",
  onFailure: async ({ payload, error, ctx }) => {
    //...
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

You can also define a global `onFailure` function using `tasks.onFailure()`.

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onFailure(({ ctx, payload, error }) => {
  console.log("Task failed", ctx.task.id);
});
```

<Info>
  Errors thrown in the `onFailure` function will be ignored, but you will still be able to see them
  in the dashboard.
</Info>

<Note>
  `onFailure` doesn’t fire for some of the run statuses like `Crashed`, `System failures`, and
  `Canceled`.
</Note>

### `catchError` functions

You can define a function that will be called when an error is thrown in the `run` function, that allows you to control how the error is handled and whether the task should be retried.

Read more about `catchError` in our [Errors and Retrying guide](/errors-retrying).

<Info>Uncaught errors will throw a special internal error of the type `HANDLE_ERROR_ERROR`.</Info>

### `onCancel` function

You can define an `onCancel` hook that is called when a run is cancelled. This is useful if you want to clean up any resources that were allocated for the run.

```ts
tasks.onCancel(({ ctx, signal }) => {
  console.log("Run cancelled", signal);
});
```

You can use the `onCancel` hook along with the `signal` passed into the run function to interrupt a call to an external service, for example using the [streamText](https://ai-sdk.dev/docs/reference/ai-sdk-core/stream-text) function from the AI SDK:

```ts
import { logger, tasks, schemaTask } from "@trigger.dev/sdk";
import { streamText } from "ai";
import { z } from "zod";

export const interruptibleChat = schemaTask({
  id: "interruptible-chat",
  description: "Chat with the AI",
  schema: z.object({
    prompt: z.string().describe("The prompt to chat with the AI"),
  }),
  run: async ({ prompt }, { signal }) => {
    const chunks: TextStreamPart<{}>[] = [];

    // 👇 This is a global onCancel hook, but it's inside of the run function
    tasks.onCancel(async () => {
      // We have access to the chunks here, and can save them to the database
      await saveChunksToDatabase(chunks);
    });

    try {
      const result = streamText({
        model: getModel(),
        prompt,
        experimental_telemetry: {
          isEnabled: true,
        },
        tools: {},
        abortSignal: signal, // 👈 Pass the signal to the streamText function, which aborts with the run is cancelled
        onChunk: ({ chunk }) => {
          chunks.push(chunk);
        },
      });

      const textParts = [];

      for await (const part of result.textStream) {
        textParts.push(part);
      }

      return textParts.join("");
    } catch (error) {
      if (error instanceof Error && error.name === "AbortError") {
        // streamText will throw an AbortError if the signal is aborted, so we can handle it here
      } else {
        throw error;
      }
    }
  },
});
```

The `onCancel` hook can optionally wait for the `run` function to finish, and access the output of the run:

```ts
import { logger, task } from "@trigger.dev/sdk";
import { setTimeout } from "node:timers/promises";

export const cancelExampleTask = task({
  id: "cancel-example",
  // Signal will be aborted when the task is cancelled 👇
  run: async (payload: { message: string }, { signal }) => {
    try {
      // We pass the signal to setTimeout to abort the timeout if the task is cancelled
      await setTimeout(10_000, undefined, { signal });
    } catch (error) {
      // Ignore the abort error
    }

    // Do some more work here

    return {
      message: "Hello, world!",
    };
  },
  onCancel: async ({ runPromise }) => {
    // You can await the runPromise to get the output of the task
    const output = await runPromise;
  },
});
```

<Note>
  You will have up to 30 seconds to complete the `runPromise` in the `onCancel` hook. After that
  point the process will be killed.
</Note>

### `onStart` function (deprecated)

<Info>The `onStart` function was deprecated in v4.1.0. Use `onStartAttempt` instead.</Info>

When a task run starts, the `onStart` function is called. It's useful for sending notifications, logging, and other side effects.

<Warning>
  This function will only be called once per run (not per attempt). If you want to run code before
  each attempt, use a middleware function or the `onStartAttempt` function.
</Warning>

```ts /trigger/on-start.ts
export const taskWithOnStart = task({
  id: "task-with-on-start",
  onStart: async ({ payload, ctx }) => {
    //...
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

You can also define a global `onStart` function using `tasks.onStart()`.

```ts init.ts
import { tasks } from "@trigger.dev/sdk";

tasks.onStart(({ ctx, payload, task }) => {
  console.log(`Run ${ctx.run.id} started on task ${task}`, ctx.run);
});
```

<Info>Errors thrown in the `onStart` function will cause the attempt to fail.</Info>

### `init` function (deprecated)

<Warning>
  The `init` hook is deprecated and will be removed in the future. Use
  [middleware](/tasks/overview#middleware-and-locals-functions) instead.
</Warning>

This function is called before a run attempt:

```ts /trigger/init.ts
export const taskWithInit = task({
  id: "task-with-init",
  init: async ({ payload, ctx }) => {
    //...
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

You can also return data from the `init` function that will be available in the params of the `run`, `cleanup`, `onSuccess`, and `onFailure` functions.

```ts /trigger/init-return.ts
export const taskWithInitReturn = task({
  id: "task-with-init-return",
  init: async ({ payload, ctx }) => {
    return { someData: "someValue" };
  },
  run: async (payload: any, { ctx, init }) => {
    console.log(init.someData); // "someValue"
  },
});
```

<Info>Errors thrown in the `init` function will cause the attempt to fail.</Info>

### `cleanup` function (deprecated)

<Warning>
  The `cleanup` hook is deprecated and will be removed in the future. Use
  [middleware](/tasks/overview#middleware-and-locals-functions) instead.
</Warning>

This function is called after the `run` function is executed, regardless of whether the run was successful or not. It's useful for cleaning up resources, logging, or other side effects.

```ts /trigger/cleanup.ts
export const taskWithCleanup = task({
  id: "task-with-cleanup",
  cleanup: async ({ payload, ctx }) => {
    //...
  },
  run: async (payload: any, { ctx }) => {
    //...
  },
});
```

<Info>Errors thrown in the `cleanup` function will cause the attempt to fail.</Info>

## Next steps

<CardGroup>
  <Card title="Triggering" icon="bolt" href="/triggering">
    Learn how to trigger your tasks from your code.
  </Card>
  <Card title="Writing tasks" icon="wand-magic-sparkles" href="/writing-tasks-introduction">
    Tasks are the core of Trigger.dev. Learn how to write them.
  </Card>
</CardGroup>
