API

Types

type EventType = string | symbol

type Handler<T> = (event?: T) => void

type WildcardHandler<T> = (type: EventType, event?: T) => void

Emitter

import { Emitter } from 'mittss'

const emitter = new Emitter(all?)

Parameters

• all Map<record<EventType, unknown>>?

  A Map of event names to registered handler functions.

on

Register an event handler for the given type.

const onWildcard = (type, ev) => {}
emitter.on('*', onWildcard)

const onFoo = ev => {}
const remove = emitter.on('foo', onFoo)
// onFoo will be removed after calling remove() function

Parameters

• type EventType | '*'

  Type of event to listen for, or '*' for all events

• handler Handler<T> | WildcardHandler<T>

  Function to call in response to given event

Returns

• remove Function

  A function to remove the event handler

off

Remove an event handler for the given type. If handler is omitted, all handlers of the given type are removed.

const onFoo = ev => {}
emitter.on('foo', onFoo)
emitter.off('foo', onFoo)

Parameters

• type EventType | '*'

  Type of event to unregister handler from, or '*'

• handler Handler<T> | WildcardHandler<T>?

  Handler function to remove

emit

Invoke all handlers for the given type. If present, '*' handlers are invoked after type-matched handlers.

Note: Manually firing '*' handlers is not supported.

const onFoo = ev => {} // ev: { foo: 'bar' }
emitter.on('foo', onFoo)
emitter.emit('foo', { foo: 'bar' })

Parameters

• type EventType

  The event type to invoke

• event any?

  Any value (object is recommended and powerful), passed to each handler

once

Invoke a handler for the given type. If present, '*' handlers areinvoked after type-matched handlers.

The handler will be removed after its first invoked.

const onFoo = ev => {} // ev: { foo: 'bar' }
emitter.once('foo', onFoo)
// emitter.all.get('foo')  return [ Function onFoo]
emitter.emit('foo', { foo: 'bar' })
// emitter.all.get('foo')  return []

Parameters

• type EventType | '*'

  The event type to invoke

• handler Handler<T> | WildcardHandler<T>

  Function to call in response to given event