data = [...]
var chart_height = 200
var bar_width = 30
var bar_gap = 10

var svg = d3.select("svg")

svg.append("defs").append("style").text(`
rect
{
fill: #6495ed;
}
rect:hover
{
fill: #000;
}
`)

svg.selectAll("rect")
.data(data)
.append("rect")
.attr("x", (d, i)=> i * (bar_width + bar_gap) )
.attr("y", (d)=>chart_height - d )
.attr("width", bar_width)
.attr("height", (d)=>d)