Courier

A tiny wrapper over the DOM CustomEvent with some additional niceties. It facilitates communication among independent or loosely coupled components. The only dependency is a shared DOM.

Setup

event-courier can be installed with npm or using a content delivery network URL to embed it on your HTML page

npm i event-courier

or

<script src="https://unpkg.com/event-courier"></script>

Usage

If installed via npm

import {
    createCourier,
    on,
    once,
    subscribe,
    emit,
    emitWithResponse,
    emitAndStore,
    emitAndStoreWithResponse
} from 'event-courier';

If loaded as a script

const {
    createCourier,
    on,
    once,
    subscribe,
    emit,
    emitWithResponse,
    emitAndStore,
    emitAndStoreWithResponse
} = Courier;

The library expose the createCourier factory function bundled with methods of the pre-made instance. That instance uses window as an event target.

import { on, emit } from 'event-courier';

or

import { createCourier } from 'event-courier';
const element = document.getElementById('elementID');
const courier = createCourier(element);
const { on, emit } = courier;

then

import { on, once, subscribe, emit } from 'event-courier';

function eventAHandler(data) {
    console.log(data); // 42 then 43
}

function oneTimeEventHandler(data) {
    console.log(data); // 42
}

function otherEventAHandler(data) {
    console.log(data); // 42 then 43
}

function eventBHandler(data) {
    console.log(data); // 44
}

once('EventA', oneTimeEventHandler);
on('EventA', eventAHandler);
subscribe({
    EventA: otherEventAHandler,
    EventB: eventBHandler
});
emit('EventA', 42);
emit('EventA', 43);
emit('EventB', 44);

Unsubscription

import { on, subscribe, emit } from 'event-courier';

function eventAHandler(data) {
    console.log(data); // 42
}

function otherEventAHandler(data) {
    console.log(data); // 42
}

function eventBHandler(data) {
    // never called
}

const unsubscribeA = on('EventA', eventAHandler);
const unsubscribe = subscribe({
    EventA: otherEventAHandler,
    EventB: eventBHandler
});
emit('EventA', 42);
unsubscribeA();
unsubscribe.EventA();
unsubscribe.EventB();
emit('EventA', 43);
emit('EventB', 44);

Saving event

import { on, emitAndStore } from 'event-courier';

function eventAHandler(data) {
    console.log(data); // 42
}
emitAndStore('EventA', 42);
setTimeout(() => {
    on('EventA', eventAHandler);
}, 1000);

The callback will be immediately called upon subscription and then on all subsequent events.

All events with the same name emitted this way are stored independently. It means that upon subscrition the callback will be called for each stored event.

import { on, emitAndStore } from 'event-courier';

function eventAHandler(data) {
    console.log(data); // 42 and 'foo'
}
emitAndStore('EventA', 42);
emitAndStore('EventA', 'foo');
setTimeout(() => {
    on('EventA', eventAHandler);
}, 1000);

Event with response

import { on, emitWithResponse } from 'event-courier';

function onEventAResponse(data) {
    console.log(data); // 43
}

function eventAHandler(data, sendResponse) {
    // no matter how the event was fired,
    // it's safe to assume that the 'senResponse'
    // is a function and always there as a second argument
    console.log(data); // 42
    sendResponse(data + 1)
}

on('EventA', eventAHandler);
emitWithResponse('EventA', 42, onEventAResponse);

Saved event with response

The combination of the two options above:

import { on, emitAndStoreWithResponse } from 'event-courier';

function onEventAResponse(data) {
    console.log(data); // 43
}

function eventAHandler(data, sendResponse) {
    // no matter how the event was fired,
    // it's safe to assume that the 'senResponse'
    // is a function and always there as a second argument
    console.log(data); // 42
    sendResponse(data + 1)
}

emitAndStoreWithResponse('EventA', 42, onEventAResponse);
setTimeout(() => {
    on('EventA', eventAHandler);
}, 1000)

Currying

All the non-unary methods of a Courier instance will be curried if you provide the second truthy argument:

const element = document.getElementById('elementID');
const { on, emit } = createCourier(element, true);

In this case you can do thing like the following:

const onEventA = on('EventA'); // will not fire an event, just returns a function
const fireEventB = emit('EventB'); // will not set a listener, just returns a function
// and then later
onEventA(data => console.log(data));
fireEventB(42);

Documentation

Please find the full docs here

License

Copyright © 2020, Sergey Chernykh. Released under the MIT License.