Edit in JSFiddle

var state = {
  count: 0
};

function reducer(state, action) {
  switch (action.type) {
    case 'increment': state.count++; break;
    case 'decrement': state.count--; break;
  }
  return state;
}

$('[data-action]').click(function(e) {
  e.preventDefault();
  render(state = reducer(state, $(this).data('action')));
});

render(state);

function render(state) {
  $('.js-target-count').text(state.count);
}

<span class='js-target-count'></span>
<button data-action='{"type":"increment"}'>+</button>
<button data-action='{"type":"decrement"}'>-</button>

body {
  background: #fff;
}

body, button {
  font: 40px/30px sans-serif;
}

button {
  background: #222;
  color: #fff;
  padding: 5px;
  border: 0;
  border-radius: 5px;
}