http://baconjs.github.io/

var up   = $('#up').asEventStream('click');

var down = $('#down').asEventStream('click');

var counter =

  // map up to 1, down to -1

  up.map(1).merge(down.map(-1))

  // accumulate sum

    .scan(0, function(x,y) { return x + y });

// assign observable value to jQuery property text

counter.assign($('#counter'), 'text');