About

Note: This library does not extend Node's EventEmitter.

A library to emit events and register listeners with the ability to define the listeners' priority.

Use cases for this :

1. Emits events and calls listeners sequentially in the order of their priority, but not wait for async listeners.
2. Same as #1 but wait for async listeners.
3. Define custom behavior for the listeners i.e. when calling emit, you can provide a arrangeListeners function to define how listeners are ordered, remove some listener by key, etc.

Sample Usage

1. Basic usage with priority (default behavior is highest priority first):

interface MyClassEvents {
  add: (el: string) => void;
  delete: (changedCount: number) => void;
}
const manager = new OrderedEventEmitter<MyClassEvents>();

//add a listener with priority 1
manager.on(
  'add',
  (el) => {
    console.log('added', el);
  },
  1,
);

//add a listener with priority 2
manager.on(
  'add',
  (el) => {
    console.log('added', 'nope');
  },
  2,
);

manager.emit({ event: 'add', priorityBehavior: 'highestFirst' }, 'hello');

// Prints
// added nope
// added hello

2. Wait for async listeners

interface MyClassEvents {
  createdProfile: (profile: { email: string }) => Promise<void>;
}
const manager = new OrderedEventEmitter<MyClassEvents>();

//add a listener with priority 1
manager.on(
  'createdProfile',
  async (profile) => {
    //Send request to third-party service. This should be last.
    return new Promise((resolve) => {
      setTimeout(() => {
        console.log('Sent request to third-party service');
        resolve();
      }, 5000);
    });
  },
  1,
);

//add a listener with priority 2
manager.on(
  'createdProfile',
  async (profile) => {
    //Notify user through email
    return new Promise((resolve) => {
      setTimeout(() => {
        console.log('Sent password email to user: ', profile.email);
        resolve();
      }, 10000);
    });
  },
  2,
);

manager.emitAsync({ event: 'createdProfile' }, { email: 'test_profile@test.com' });

// Prints
// Sent password email to user: test_profile@test.com
// Sent request to third-party service

3. Custom ordering of listeners

interface MyClassEvents {
  add: (el: string) => void;
  delete: (changedCount: number) => void;
}
const manager = new OrderedEventEmitter<MyClassEvents>();

//add a listener with priority 1
manager.on(
  'add',
  (el) => {
    console.log('added', el);
  },
  1,
  'add1',
);

//add a listener with priority 2
manager.on(
  'add',
  (el) => {
    console.log('added', 'nope');
  },
  2,
  'add2',
);

manager.emit(
  {
    event: 'add',
    arrangeListeners: (listeners) => {
      //remove listener with key of `add2`
      return listeners.filter((listener) => listener.key !== 'add2');
    },
  },
  'hello',
);

// Prints
// added hello