mercury / vdom compatible event for taking a firehose of events and reducing to the ones you want.

I was working on an app where I need to capture just the focus events (focusin, focusout) for a given input, then modify state. When using value-event/event, I can broadcast and receive the event, but this has 2 problems:

1. Since the original event object and DOM element are de-coupled, it is not possible to know the type of event fired. I just know that there was AN event.
2. A large number of events are being fired. Most of them are not important to me.

Added value-event/filter event. This works exactly like value-event/eventexcept that it takes a whitelist of event names that it will allow to pass. This allows event targeting without bringing any part of the event or DOM forward into the handler or channel.

var sendFilteredEvent  = require('value-event/filter.js');

var state = { 
  active: false
};
var active_handler = function(active) {
  state.active = active;
};
var text_handlers = [

  sendFilteredEvent(active_handler, true , {
    event_types: ['focusin']
  }), 

  sendFilteredEvent(active_handler, false, {
    event_types: ['focusout']
  })
];

Now the VDOM part

h('input', {
  'ev-event': text_handlers,
  name: 'dogs',
  type: 'text'
});