    
        var resetCssClasses = function(activeEl) {
        var els = document.querySelectorAll('button')
        Array.prototype.forEach.call(els, function(el) {
          el.classList.remove('active')
        })
      
        activeEl.target.classList.add('active')
      }
      
      document
        .querySelector('#one_month')
        .addEventListener('click', function(e) {
          resetCssClasses(e)
      
          chart.zoomX(
            new Date('28 Jan 2013').getTime(),
            new D