KeepLatest task

This is the way to create a keepLatest task.

This will run the initial tasks and then, if over the max concurrency will keep the very last instance in a que. You can also provide a max that will dictate the number of task instances that will run initially.

Note

keepLatest will only preserve the final one task instance.

Usage

To specify a task as keepLatest, you can either use the dot notation or the options notation.

Dot notation

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

const latestTask = task.keepLatest(async () => {
  // your code
});

Options notation

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

const latestTask = task(
  async () => {
    // your code
  },
  { kind: 'keepLatest' },
);

Max concurrency

This is how you can specify the maximum number of concurrent instances. The default is 1, here we’re setting it to 5.

Note

max here denotes the number of task instances that will run initially, it will always keep the lastest one instance when the max threshold is exceeded.

Dot notation

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

const latestTask = task.keepLatest(
  async () => {
    // your code
  },
  { max: 5 },
);

Options notation

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

const latestTask = task(
  async () => {
    // your code
  },
  { kind: 'keepLatest', max: 5 },
);

The task

The return value of the task function will be an object with getters where you can access state from all the instances running and eventually cancel them with cancelAll.

Task structure Take a look at the Task structure documentation in our Getting started

Passing props

While defining a task, if the function that you pass in has some arguments, those will be required by the perform function (and it will be strongly typed too).

Caution

If you need to pass multiple props you should use an object because the second parameter will always be the SheepdogUtils.

Dot notation

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

const latestTask = task.keepLatest(async (id: string) => {
  // your code
});

button.addEventListener('click', () => {
  latestTask.perform('42');
});

Options notation

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

const latestTask = task(
  async (id: string) => {
    // your code
  },
  { kind: 'keepLatest' },
);

button.addEventListener('click', () => {
  latestTask.perform('42');
});

Getting the return value

If you return something from your task you can access the return value by awaiting the perform function.

Dot notation

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

const latestTask = task.keepLatest(async () => {
  return 42;
});

button.addEventListener('click', () => {
  const number = await latestTask.perform();
  console.log(number); // 42
});

Options notation

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

const latestTask = task(
  async () => {
    return 42;
  },
  { kind: 'keepLatest' },
);

button.addEventListener('click', () => {
  const number = await latestTask.perform();
  console.log(number); // 42
});

Getting the TaskInstance

If you don’t await the perform function, then you’ll get back the task instance that you can use either to cancel it or to get its current state. The TaskInstance is also an object with getters you can access the current value with instance.value or register events on it with instance.on.

Dot notation

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

const latestTask = task.keepLatest(async () => {
  // your code
});

button.addEventListener('click', () => {
  const lastRun = latestTask.perform();
  lastRun.on('success', () => {
    console.log(lastRun.value);
  });
  lastRun.cancel();
});

Options notation

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

const latestTask = task(
  async () => {
    // your code
  },
  { kind: 'keepLatest' },
);

button.addEventListener('click', () => {
  lastRun = latestTask.perform();
  lastRun.on('success', () => {
    console.log(lastRun.value);
  });
  lastRun.cancel();
});