Task Instance

Structure

To standardize the approach regardless of which task modifier you’re using, every task modifier will use the same underlying TaskInstance structure (which is a stateful class).

A TaskInstance comprises of:

• error: if an error is thrown inside the task instance, it will be found here
• value: if the task instance completed successfully, this will be the return value
• on: a function to add a listener on the task instance itself, the events you can listen for are:
  • error: emitted by the instance when an error is thrown during the run
  • finish: emitted by the instance when for whatever reason it finishes (either if it errors, is being canceled or it complete successfully)
  • cancel: emitted by the instance when the task is canceled
  • start: emitted by the instance when the task actually starts (it could be canceled before this event is emitted)
  • success: emitted by the instance when the execution terminates without erroring out or being canceled

And for those of you that prefer to read code, here is the typing of the TaskInstance:

type TaskInstance<TReturn> = {
  /**
   * If an error is thrown inside the task instance, it will be found here.
   */
  error?: Error;

  /**
   * If the task instance completed successfully, this will be the return value.
   */
  value?: TReturn;

  /**
   * A function to add a listener on the task instance itself, the events you can listen for are:
   *
   * - error
   * - finish
   * - cancel
   * - start
   * - success
   */
  on: (event: InstanceEvents, cb: () => void, options?: AddEventListenerOptions) => void;
};

where InstanceEvents is:

type InstanceEvents = 'error' | 'finish' | 'cancel' | 'start' | 'success';

Cancellation

Each task instance is also packaged with a cancel function that can be used to cancel itself.

import { task } from '@sheepdog/svelte';

const myTask = task(async () => {
  // your code
});

let lastInstance;

button.addEventListener('click', () => {
  lastInstance = myTask.perform();
});

cancelLast.addEventListener('click', () => {
  lastInstance?.cancel();
});