switchboard

// switchboard.js

A composite event listener. Waits for several events to occur before firing the handler.

Switchboard returns the arguments of each respective emit to the specified handler. These arguments can be named if desired.

Installing

node.js:

npm install switchboard

bower:

bower install switchboardjs

<script src="components/switchboardjs/index.js"></script>

Why do I need this?

Sometimes you have to wait for 2 or more things to happen before a certain part of your program can move forward. Let's say you're rendering a bunch of templates, for example. You want to do it asynchronously, but it's kind of a pain to figure out when everything's done without something kludgey (like a static counter or a jungle of if statements). switchboard.js can hide the kludge for you.

Familiar syntax, too. Just uses the classic EventEmitter 'on/once' pattern. Except instead of a single event name, you specify an array.

How to use

You've got two choices, cowboy.

1. Extremely simple way

var Switchboard = require('switchboard').Switchboard,
    myEmitter   = new Switchboard();

var events = ['firstEvent', 'secondEvent', 'thirdEvent'];

myEmitter.on(events, function(args) {
  // after calling `myEmitter.emit(e)` for all three events, args is something like:
  // { 'firstEvent':  [ ... the args ... ],
  //   'secondEvent': [ ... the args ... ],
  //   ...
  // }
  // etc.
});

2. With a little bit more code, you get your results returned in a dictionary!

var Switchboard = require('switchboard').Switchboard,
    myEmitter   = new Switchboard();

var events = ['firstEvent', 'secondEvent', 'thirdEvent'];

myEmitter.registerEventArguments({
  firstEvent: ['err', 'resultA', 'resultB']
});

// multiple calls to registerEventArguments are a-okay
// (hint: good for loops or for registering callbacks from
// within other callbacks)
myEmitter.registerEventArguments({
  secondEvent: ['resultC', 'resultD', 'resultE'],
  thirdEvent:  ['err', 'myVar', 'someJunk']
});

myEmitter.once(events, function(args) {
  console.log(args)
});

Now that you've defined your events, you can go ahead and emit things...

myEmitter.emit('firstEvent', null, 'aaaa', 'bbbbb')
myEmitter.emit('thirdEvent', {err: 'someErr'}, 'mvvvarrr', 'junk~!')
myEmitter.emit('secondEvent', 'CCCC', 222222, 'EEEE')

Which will produce the following output:

{ firstEvent: 
  { '0': null,
    '1': 'aaaa',
    '2': 'bbbbb',
    err: null,
    resultA: 'aaaa',
    resultB: 'bbbbb' },
secondEvent: 
  { '0': 'CCCC',
    '1': 222222,
    '2': 'EEEE',
    resultC: 'CCCC',
    resultD: 222222,
    resultE: 'EEEE' },
thirdEvent: 
  { '0': { err: 'someErr' },
    '1': 'mvvvarrr',
    '2': 'junk~!',
    err: { err: 'someErr' },
    myVar: 'mvvvarrr',
    someJunk: 'junk~!' } }

As you can see, each event's arguments are enumerated as well as being named. The point: you can skip the call to registerEventArguments() if you want.