evx

Handy dandy persistent-state pub/sub with multi, wildcard, and single-property subscriptions. 400 bytes gzipped.

Install

npm i evx --save

Usage

evx is just a simple pub/sub bus:

import { on, emit } from 'evx'

on('foo', () => console.log('foo was emitted!'))

emit('foo')

But it also allows you to subscribe to multiple events at once:

// fires once
on(['foo', 'bar'], () => console.log('foo or bar was emitted!'))

emit('bar')

And emit multiple events at once:

// fires twice
on(['foo', 'bar'], () => console.log('foo or bar was emitted!'))

emit([ 'bar', 'foo' ])

It has wildcard support:

on('*', () => console.log('an event was emitted!'))

emit('baz')

Additionally, you can subscribe to specific property values by passing the property key as the event name:

on('someProperty', state => {}) // someProperty updated

emit('foo', { someProperty: true }) // will fire
hydrate({ someProperty: true })() // will also fire

State

Additionally, it has a concept of state. In evx state is always an object. Any object passed to emit will be shallowly merged with global state:

emit('foo', { value: true })

And all subscribers are passed the full state object:

on('foo', state => console.log(state.value)) // true

To emit transient data that does not get merged into the global state, pass an object as the third argument to emit:

emit('event', null, { message: 'Hello' })

And access via the second argument subscribers:

on('event', (state, data) => console.log(data.message)) // Hello

If you need to add some state but don't want to emit any events, use hydrate:

import { hydrate } from 'evx'

hydrate({ baz: true })

But for convenience, hydrate also returns a function that, when called, will emit a '*' event:

hydrate({ baz: true })()

The current read-only state is accessible as well:

import { hydrate, getState } from 'evx'

hydrate({ baz: true })

getState() // { baz: true }

Cleanup

Subscribers return a function that will unsubscribe from that event:

const unsubscribe = on('foo', () => {})

emit('foo') // will fire

unsubscribe()

emit('foo') // will not fire

Multiple instances

If you need to create a discrete instance of evx, use create:

import { create } from 'evx'

const bus = create()

All methods above are now accessible on bus.

You can also pass an optional initial state object to create:

const bus = create({ foo: 'hello' })

License

MIT License © Eric Bailey