codepen zoomer

penzoom.js

var $results = $('#result_div');
var button = document.createElement('button');
button.className = 'top-button button';
button.innerHTML = 'Zoom';

var toggleZoom = function() {
  var result_height = $results.attr('data-height');

  $('.top-boxes, .resizer').toggle();

  if (result_height) {
    $results.height(result_height);
    $results.removeAttr('data-height');
  }
  else {
    $results.attr('data-height', $results.height());
    $results.height('100%');
  }
};

button.onclick = toggleZoom;

$('.box-actions').append(button);