Observing your composition

A compose chain emits lifecycle events: start, complete, task failure. .meta({ name, hooks }) attaches callbacks for each: onStart, onComplete, onTaskFail. The name identifies each chain in logs and metrics.

Hooks

onStart

Fires when the compose chain starts.

import { compose, createTask } from "@grlt-hub/app-compose"

const auth = createTask({
  name: "auth",
  run: {
    fn: () => {
      console.log("auth ran")
      return { id: 1 }
    },
  },
})

compose()
  .meta({
    name: "auth-page",
    hooks: {
      onStart: (event) => {
        console.log(`${event.meta?.name} started`)
      },
    },
  })
  .step(auth)
  .run()

onComplete

Fires when the compose chain completes.

import { compose, createTask } from "@grlt-hub/app-compose"

const auth = createTask({
  name: "auth",
  run: {
    fn: () => {
      console.log("auth ran")
      return { id: 1 }
    },
  },
})

compose()
  .meta({
    name: "auth-page",
    hooks: {
      onComplete: (event) => {
        console.log(`${event.meta?.name} completed`)
      },
    },
  })
  .step(auth)
  .run()

onTaskFail

Fires when a task inside the compose chain fails.

import { compose, createTask } from "@grlt-hub/app-compose"

const auth = createTask({
  name: "auth",
  run: {
    fn: () => {
      throw new Error("Ooops!")
    },
  },
})

compose()
  .meta({
    name: "auth-page",
    hooks: {
      onTaskFail: (event) => {
        console.log(`Task ${event.task.name} failed`)
        console.log(`With an error: ${event.error}`)
      },
    },
  })
  .step(auth)
  .run()

Nested compose

Event bubbling