Create Reusable Tasks

To create task functions that can be used across multiple flows without tight coupling to specific flow structures.

Steps

1. Define task parameters

   Identify exactly what data the task needs to function. Accept specific parameters, not entire input objects:

   // ✅ Accept specific parameters
   async function fetchUserProfile(userId: string) {
     const response = await fetch(`https://api.example.com/users/${userId}`);
     return response.json();
   }
   
   // ❌ Don't accept entire input object
   async function fetchUserProfile(input: { user: { id: string }) {
     const response = await fetch(`https://api.example.com/users/${input.user.id}`);
     return response.json();
   }

2. Return JSON-serializable data

   Return primitives, plain objects, or arrays. Convert dates to ISO strings:

   async function fetchUserProfile(userId: string) {
     const response = await fetch(`https://api.example.com/users/${userId}`);
     const user = await response.json();
     return {
       id: user.id,
       name: user.name,
       email: user.email,
       createdAt: new Date(user.created_at).toISOString() // Convert to ISO string
     };
   }

3. Use step handlers as adapters

   Let the flow’s step handler extract needed data from the flow context:

   // Your task function
   async function fetchUserProfile(userId: string) {
     const response = await fetch(`https://api.example.com/users/${userId}`);
     return response.json();
   }
   
   // Flow uses handler to adapt context to task parameters
   new Flow<{ userId: string }>({ slug: 'user_flow' })
     .step({ slug: 'profile' }, async (input) =>
       await fetchUserProfile(input.run.userId)
     )

4. Test in isolation

   Verify the task works independently of any flow:

   tasks/fetchUserProfile.test.ts

   import { assertEquals } from "jsr:@std/assert";
   import { fetchUserProfile } from "./fetchUserProfile.ts";
   
   Deno.test("fetches user profile", async () => {
     const result = await fetchUserProfile("user_123", "test-key");
   
     assertEquals(result.id, "user_123");
     assertEquals(result.name, "Alice Johnson");
     assertEquals(result.email, "[email protected]");
     assertEquals(result.createdAt, "2024-01-15T10:30:00.000Z");
   });

Learn More

Organize Flow Code Learn where to put your task files and structure your codebase

Context Object Understanding the context parameter available to handlers

See it in Action

AI Web Scraper Tutorial Complete example showing reusable tasks in a real-world flow