npm install --save event-chain

var chain = require('event-chain')();

var example = chain.on(['one', 'two'], function() {
  console.log('foo');
});

example.emit('one');
example.emit('two');
// foo to console.

env DEBUG=event-chain

/**
 * Create an event-chain that will execute the callback after all the events have been emitted.
 *
 * @param events
 *   An array of events (string) that are required before invoking the callback.
 * @param callback
 *   A callback function to be executed after all the provided events have been fired.
 *
 * @return
 *   A Chain object.
 */
chain.on(events, callback)

/**
 * Emit the given event for the chain.
 *
 * @param event
 *   Emit an event that was previously registered with chain.on();
 */
foo.emit(event);

var chain = require('event-chain')(options);

The event that is fired once all user-defined events have completed, used internally. Default: '__complete'