Currently, our bars have a fixed width. No matter how many elements we have, they have a 15 px width. If we had more data elements, the bars could overlap. Let's change this. Since each rect will be the same width, no matter what the data is, we can just assign width a computed value. Add the following to the end of the AJAX callback:

d3.selectAll('rect')
    .attr('width', WIDTH/data.length);

Now let's adjust our rect CSS so our bars are more visible:

rect {
    /*  remove the width rule that was here */
    stroke:white;
    stroke-width:1px;
}