eventflow

Flow control for your event emitters

EventFlow

Flow control for your event emitters.

EventEmitters are an important part of well-designed node.js applications. on() and emit() can get you pretty far, but wouldn't it be great if you could run your event handlers asynchronously, with a continuation callback.

EventFlow adds the flow-controlly-goodness of async to your event emitters.

Attach eventflow to your event emitter:

var EventEmitter = require('events').EventEmitter,
    require('eventflow')(EventEmitter),
    emitter = new EventEmitter();

Or, if you prefer not to extend the prototype:

var EventEmitter = require('events').EventEmitter,
    emitter = new EventEmitter();
 
require('eventflow')(emitter);

Listen for some events, with or without continuation callbacks. EventFlow does some simple introspection of your listeners to see if they accept a callback or not.

emitter.on('foo', function() {
  // Do something synchronous 
});
 
emitter.on('foo', function(callback) {
  doSomethingAsync(function(bar) {
    callback();
  });
});

Now use one of the flow control methods to invoke your handlers and respond when they are done.

series

emitter.series('foo', function() {
  // The listeners ran in the order they were added and are all finished. 
});

parallel

emitter.parallel('foo', function() {
  // The listeners ran in parallel and are all finished. 
});

Event listeners with arguments

EventFlow supports calling your listeners with any number of arguments, as well as the optional continuation callback.

// In your logger or something: 
emitter.on('purchase', function(nameitemcost) {
  console.log(name + ' just bought ' + item + ' for ' + cost);
})
 
// Somwhere else in your code: 
emitter.on('purchase', function(nameitemcostcallback) {
  saveToDB({name: name, item: item, cost: cost}, callback);
});
 
// Perhaps in a form POST handler: 
emitter.series('purchase', 'Brian', 'T-Shirt', '$15.00', function() {
  // The purchase was logged and saved to the db. 
});

Using async-style callback(err, results)

EventFlow uses async directly to handle the flow-control, so you can use err and results just like you already do.

// Synchronous listeners can return a result. 
emitter.on('fruit', function() {
  return 'apple';
});
 
// Async listeners use the standard (err, result) callback. 
emitter.on('fruit', function(callback) {
  callback(null, 'orange');
});
 
emitter.series('fruit', function(errresults) {
  console.log(results);
  // [ 'apple', 'orange' ] 
});

Developed by Terra Eclipse

Terra Eclipse, Inc. is a nationally recognized political technology and strategy firm located in Aptos, CA and Washington, D.C.

http://www.terraeclipse.com

Copyright (C) 2012 Terra Eclipse, Inc.

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