@nichoth/events

An event bus and helpers

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Readme

events

An event bus and helpers

install

$ npm install @nichoth/events

bus

This inherits from nanobus, and has the same API, plus some additional stuff:

  • You can pass in list of valid event names, and will throw if you emit or listen for a bad event name
  • The emit method will return a curried function if you don't pass a second argument
  • You can pass in { memo: true }, which will memoize any curried emit functions instead of creating a new function each time

example

event emitter

Pass in a list of event names when you create a bus, then throw an error if you subscribe to an event that's not in the list. If you don't pass in any event names, then you can subscribe to anything.

var test = require('tape')
var Bus = require('../')

// create a new instance
var bus = Bus({
    eventNames: ['hello'],  // optional allowed event names
    memo: false  // return memoized emit function, default false
})

test('bad event name', function (t) {
    t.plan(1)
    try {
        bus.on('foo', () => console.log('foo'))
    } catch (err) {
        t.equal(err.message, 'Invalid event name foo')
    }
})

test('good event name', function (t) {
    t.plan(1)
    bus.on('hello', function (data) {
        t.equal(data, 'world', 'subscriptions work')
    })
    bus.emit('hello', 'world')
})

test('dont throw if given no event names', function (t) {
    t.plan(1)
    var bus = Bus()
    bus.on('foo', function (data) {
        t.equal(data, 'bar')
    })
    bus.emit('foo', 'bar')
})

emit method

Return a curried function if you don't pass in a second argument, and optionally cache the emit functions if opts.memo === true.

test('curry emit method', function (t) {
    t.plan(1)
    var bus = Bus()
    bus.on('foo', function (data) {
        t.equal(data, 'hello')
    })
    var emitFoo = bus.emit('foo')
    emitFoo('hello')
})

test('memoize the emitters', function (t) {
    t.plan(2)
    var bus = Bus({
        memo: true
    })

    var emitBar = bus.emit('bar')
    var emitBar2 = bus.emit('bar')
    var emitBar3 = bus.emit('bar')

    t.equal(emitBar, emitBar2, 'should return the same reference')
    t.equal(emitBar, emitBar3, 'should return the same reference')
})

namespace

Recursively namespace an object of event names

example

var namespace = require('@nichoth/events/namespace')
var test = require('tape')

var input = {
    events: {
        update: ['get', 'add', 'delete', 'edit'],
    },

    foo: {
        bar: {
            baz: ['a', 'b', 'c']
        }
    }
}

var expected = {
    events: {
        update: {
            get: 'events.update.get',
            add: 'events.update.add',
            delete: 'events.update.delete',
            edit: 'events.update.edit'
        }
    },
    foo: {
        bar: {
            baz: {
                a: 'foo.bar.baz.a',
                b: 'foo.bar.baz.b',
                c: 'foo.bar.baz.c'
            }
        }
    }
}

test('namespace', function (t) {
    t.plan(1)
    t.deepEqual(namespace(input), expected)
})

flatten

Take an object of strings and return an array of the leaf nodes. The object can be any depth.

example

var flatten  = reuqire('@nichoth/events/flatten')
var test = require('tape')

test('flatten', function (t) {
    t.plan(1)
    t.deepEqual(flatten(namespace(input)), [
        'events.update.get',
        'events.update.add',
        'events.update.delete',
        'events.update.edit',
        'foo.bar.baz.a',
        'foo.bar.baz.b',
        'foo.bar.baz.c'
    ])
})

http

Take an async function and return a new function that emits events on the given bus

example

var HttpEffects = require('../http')
var Bus = require('../')
var test = require('tape')

test('http effects', function (t) {
    t.plan(2)
    var bus = Bus()
    var fns = {
        foo: function (arg, cb) {
            process.nextTick(function () {
                cb(null, 'world')
            })
        },

        err: function (arg, cb) {
            process.nextTick(function () {
                cb('test')
            })
        }
    }

    var evs = {
        start: 'start',
        error: 'error',
        resolve: 'resolve'
    }

    var result = []
    // the last argument is data that gets added to the event objects
    var fooFx = HttpEffects(evs, bus, fns.foo, {})

    bus.on('*', function (ev, data) {
        result.push([ev, data])
        if (result.length === 4) {
            t.deepEqual(result, [
                ['start', { cid: 0, req: 'hello' }],
                ['start', { cid: 1, req: 'test' }],
                ['resolve', {
                    cid: 0, res: 'world', req: 'hello' }],
                ['resolve', {
                    cid: 1, res: 'world', req: 'test' }],
            ], 'should emit the right events')
            bus.removeAllListeners()
            testErr()
        }
    })

    fooFx('hello')
    fooFx('test')

    function testErr () {
        var errResult = []
        bus.on('*', function (ev, data) {
            errResult.push([ev, data])
            if (errResult.length === 2) {
                t.deepEqual(errResult, [
                    ['start', { cid: 2, req: {} }],
                    ['error', { cid: 2, req: {}, error: 'test'}]
                ], 'request with error response')
            }
        })
        HttpEffects(evs, bus, fns.err, {}, {})
    }
})

subscription

Subscribe to events and call methods with the right context

example

constructor

var Sub = require('../subscribe')
var assert = require('assert')
var Store = require('@nichoth/state')
var Bus = require('../')

var DemoStore = Store.extend({
    _state: { hello: 'world', calls: { foo: 0, bar: 0, baz: 0 } },
    foo: function (data) {
        this._state.calls.foo++
        this._state.hello = data
    },
    bar: function (data) {
        this._state.calls.bar++
        this._state.hello = data
    },
    baz: function (data) {
        this._state.calls.baz++
        this._state.hello = 'baz' + data
    }
})

// the constructor takes a context object, an event emitter, and
// an optional third object with fields that will be added to `this`
var bus = Bus()
var demoStore = DemoStore()
var sub = Sub(demoStore, bus, { events: { foo: 'foo' } })

.on(String eventName, String | method fn) => subscription

Listen for events and call methods with the right context

var sub = Sub(demoStore, bus)
    .on('example', 'foo')
    .on('woo', demoStore.bar)

bus.emit('example', 'again')
console.log(demoStore.state().hello)
assert.equal(demoStore.state().hello, 'again',
    'should call method by string')

bus.emit('woo', 'moo')
console.log(demoStore.state().hello)
assert.equal(demoStore.state().hello, 'moo', 'should call fn')

// you can only have 1 listener per event
// new functions will replace the previous one
sub.on('example', 'baz')
bus.emit('example', 'hey')
console.log('replace', demoStore.state())
assert.equal(demoStore.state().calls.foo, 1)
assert.equal(demoStore.state().calls.baz, 1)

.close() => undefined

Remove all event listeners

sub.close()
bus.emit('example', 'test')
console.log(demoStore.state().hello)
assert.equal(demoStore.state().hello, 'moo', 'should unsubscribe')

Subscription.extend (function fn, object opts) => Subscription

Helper that extends Subscription by calling fn during construction, and extending the prototype with opts

var MySubscription = Subscription.extend(function () {
    this.on('foo', 'bar')
}, { map: ev => ev.value })

var sub = MySubscription(demoStore, bus)
bus.emit('foo', 'new data')
assert.equal(demoStore.state().hello, 'new data', 'should subscribe')

.map (data, eventName, methodName) => any

this.map is called with the value of any event, and the return value is passed to the store method. It defaults to the identity function a => a

// override the parent's map function
var MapExample = ExampleSub.extend({
    map: function (data, evName, method) {
        assert.deepEqual(data, { value: 'foo' })
        assert.equal(evName, 'example.foo')
        assert.equal(method, 'foo')
        return data.value
    }
})

var mapExampleStore = DemoStore()
var mapExample = MapExample(mapExampleStore, bus, {
    evs: { foo: 'example.foo', bar: 'example.bar' }
})

bus.emit('example.foo', { value: 'foo' })
assert.deepEqual(mapExampleStore.state(), {
    hello: 'foo',
    calls: { foo: 1, bar: 0, baz: 0 }
})

mapExample.close()

If you find any bugs or have a feature request, please open an issue on github!

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