Xazure Event Manager

An async-first event manager. Used by Xazure CMS.

Uses an async reducer pattern to parse arguments with all events.

Basic Usage

import EventManager from 'xazure-event-manager';

const eventManager = EventManager();

// Add event
eventManager.add('add', async previous => {
  const args = await previous;
  const { a, b, sum = 0 } = args;
  return Object.assign(args, { sum: sum + a + b });
});

// in an async function
// Apply event
const { a, b, sum } = await eventManager.apply('add', { a: 1, b: 2 });

Concepts

Xazure Event Manager is async-first. All of the event callbacks should accept a Promise which resolves an object with the parameters. This allows any event to be asynchronous without any additional effort.

eventManager.add('add', async previous => {
  const args = await previous;
}); 

The event manager will run through each event in priority order:

eventManager.add('rollCall', [
  Object.assign(
    async previous => {
      const args = await previous;
      return Object.assign(args, { list: [].concat(args.list, 'a') });
    }, { priority: 1 }
  ),
  Object.assign(
    async previous => {
      const args = await previous;
      return Object.assign(args, { list: [].concat(args.list, 'b') });
    }, { priority: 2 }
  ),
  Object.assign(
    async previous => {
      const args = await previous;
      return Object.assign(args, { list: [].concat(args.list, 'c') });
    }, { priority: 3 }
  )
]);

const { list } = eventManager.apply('rollCall');
console.log(list); // ['a', 'b', 'c']

Each event should return all of the arguments, making any transforms as necessary.

Any event can return a Promise or the arguments directly.

API

add(eventName, callback, priority)

• eventName - string - The event name to register.
• callback - function(Promise<{}>):(Promise<{}>|{}) - The callback function to call, or an array of them.
• priority - number - Optional. Specifies the priority. Default: 100

callback should accept a Promise as it's only parameter, which will resolve to an object of arguments. It should return the arguments object, applying any required transforms, or a Promise that results in one.

callback can also have a static priority value. If provided, it supersedes the priority argument given to the function. This is useful when passing an array where you want different priorities.

If neither callback.priority or priority are given, it'll be defaulted to 100.

addMap(map)

Registers a map of events, with each key being the event name, and the values the callback(s).

See add() for rules on the callbacks.

apply(eventName, args = {}):Promise<{}>

Applies the arguments to all registered events for the given name, in priority order (ascending).

The args are given to the first callback (wrapped in a Promise), then the result of that is given to the next and so-on (a reducer pattern).