@harlem/extension-action

Harlem Action Extension

This is the official action extension for Harlem. This extension adds asynchronous action capabilities to your store. Some of the features of this extension are:

• Cancellable (incl. nested actions)
• Direct mutations within the action body - no need to specify a separate mutation
• Decoupled status checks through helper functions (isActionRunning and hasActionRun)

Getting Started

Follow the steps below to get started using the action extension.

Installation

Before installing this extension make sure you have installed @harlem/core.

Install @harlem/extension-action:

npm install @harlem/extension-action

Or if you're using Yarn:

yarn add @harlem/extension-action

Registration

To get started simply register this extension with the store you wish to extend.

import actionExtension from '@harlem/extension-action';

import {
    createStore
} from '@harlem/core';

const STATE = {
    firstName: 'Jane',
    lastName: 'Smith'
};

const {
    state,
    getter,
    mutation,
    action,
    hasActionRun,
    isActionRunning,
    whenActionIdle,
    clearActionRunCount
} = createStore('example', STATE, {
    extensions: [
        actionExtension()
    ]
});

The action extension adds 5 new methods to the store instance: action, hasActionRun, isActionRunning, whenActionIdle and clearActionRunCount.

Usage

Defining an action

An action can be defined the same way you define any other core functionality (eg. getter, mutation etc.).

export default action('load-user-data', async (id: number, mutate, controller) => {
    const userData = await fetch(`/api/user-data/${id}`, {
        signal: controller.signal
    });

    mutate(state => Object.assign(state.details.user, userData));
});

The action implementation is very similar to the core mutation method with some minor differences - The body of the action method is async, includes a mutate method and controller parameter.

You can also return data from the action body.

Mutate

The mutate method supplied to the action body is the equivilent of defining a mutation with the same name and no payload. This is a convenient alternative to defining a separate mutation.

The only parameter supplied to the mutate callback is a writable version of state.

Controller

The controller parameter supplied to the action body is an instance of an AbortController. The controller is used as a cancellation token for handling when the action is cancelled. This is particularly useful for terminating fetch requests in actions.

Specifying action options

The third argument to the action body is an options object.

export default action('load-user-data', async (id: number, mutate, controller) => {
    ...
}, {
    parallel: true
});

• parallel: boolean - indicates whether this action allows multiple instances running in parallel. This is set to false by default meaning any instance of this action that starts while another is running will cause the already running action to abort.

Calling an action

To call an action simply import it and call it with the payload (if a payload type is defined).

import {
    loadUserData
} from './actions';

async function runAction() {
    await loadUserData(85);
}

Cancelling an action

Each time an action is called it returns an instance of a Task class. The Task class is an extension of the in-built Promise class that adds an abort method you can use to terminate the action.

async function runAction() {
    const task = loadUserData(85);

    setTimeout(() => task.abort(), 1000);

    await task;
}

Cancelling the task will throw an ActionAbortError. It is recommended to wrap actions you intend on cancelling in a try/catch statement to handle this.

Handling nested actions

Using nested actions is as simple as calling any other action(s) within the body of the current action. However, to handle cancellation through nesting, the parent controller needs to be passed down to the nested instance(s).

import {
    childAction1,
    childAction2,
} from './child-actions';

export default action('parent-action', async (id: number, mutate, controller) => {
    await Promise.all([
        childAction1('payload', controller),
        childAction2('payload', controller),
    ]);
});

Checking action status

This extension provides a set of helper methods for checking the status of actions. There are 2 ways to check whether an action is running:

• Direct
• Indirect

The direct method is simply awaiting the task that is returned from calling the action:

async function runAction() {
    await loadUserData(85);
}

The indirect method is using the helper methods on the store to check whether the action is currently running or has run at all.

To check whether the action is currently running use the isActionRunning method:

const isRunning = computed(() => isActionRunning('load-user-data'));

To check whether the action has run at all use the isActionRunning method:

const isRunning = computed(() => hasActionRun('load-user-data'));

To respond to when an action becomes idle use the whenActionIdle method:

await whenActionIdle('load-user-data');

All of these methods accept an optional predicate function as the second argument. The predicate function is used to check the status of a particular instance of that action. for example, say you call the same action with 2 different payloads:

loadUserData(85);
loadUserData(88);

const isFirstActionRunning = isActionRunning('load-user-data', payload => payload === 85);

The predicate function is called with the payload for each instance of the action currently running. The predicate function must return a boolean.

Changelog

2.0.0-beta.7 (2021-09-07)

Bug Fixes

• action: return function as devtools value (b7efd94)
• devtools: send inspector tree on manual devtools update (97e7203)