Bar chart test 13 & 14

I am almost done with my bar chart…but I can’t seem to pass the last two tests. I am trying to add a basic tooltip using .append('title) but can’t seem to get it to work

here is my code that I am trying to get to work

  .on('mouseover', d=>{ // how to get tool tip to work
  d3.select(this).append('title').attr('id','tooltip')
  .append('text')
  .attr('data-date', d=>d[0])
  .text(d[0])
})

and the link to the codepen: https://codepen.io/anon/pen/vQeBQx/?editors=0010