code: function doScroll (node, val, finish) {
    if (!val) {
      return
    }
    if (finish === undefined) {
      finish = Math.abs(val)
    }
  
    if (finish <= 0) {
      return
    }
  
    setTimeout(function () {
      if (val > 0) {
        node.scrollLeft += 2
      }
      else {
        node.scrollLeft -= 2
      }
      finish -= 2
  
      doScroll(node, val, finish)
    })
  }
docs: scroll the tabheader. positive val means to scroll right. negative val means to scroll left.