D3 Examples - Horizontal Bar Chart with Tooltip D3 V4

Horizontal Bar Chart with Tooltip D3 V4
This chart shows average house prices in various areas of Liverpool, UK
d3.json - load and parse data
d3.tickFormat - format y axis tick text
d3.max - compute domains
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<!DOCTYPE html>
<meta charset="utf-8">
<head>
  <link href="https://fonts.googleapis.com/css?family=Fira+Sans:300,300i,400,500,700" rel="stylesheet">
</head>
<style>
body {
  margin: 15px;
  background-color: #F1F3F3;
  font-family: 'Fira Sans', sans-serif;
}
.bar {
    fill: #6F257F;
}
.bar:hover {
    fill: #CC0058;
  transition: fill 0.15s;
}
text {
  font-family: 'Fira Sans', sans-serif;
  font-weight: 500;
  font-size: 15px;
  color: #081F2C;
}
.axis path,
.axis line {
  fill: none;
  stroke: #BDC2C6;
  stroke-width: 1px;
  shape-rendering: crispEdges;
}
.x path {
    display: none;
}
.y line {
  display: none;
}
.toolTip {
    position: absolute;
  pointer-events: none;
  display: none;
  min-width: 50px;
  height: auto;
  background: none repeat scroll 0 0 #ffffff;
  padding: 9px 14px 6px 14px;
  border-radius: 2px;
  text-align: center;
  line-height: 1.3;
  color: #5B6770;
  box-shadow: 0px 3px 9px rgba(0, 0, 0, .15);
}
.toolTip:after {
  content: "";
  width: 0;
  height: 0;
  border-left: 12px solid transparent;
  border-right: 12px solid transparent;
  border-top: 12px solid white;
  position: absolute;
  bottom: -10px;
  left: 50%;
  margin-left: -12px;
}  
.toolTip span {
    font-weight: 500;
  color: #081F2C;
}
</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
var svg = d3.select("svg"),
    margin = {top: 20, right: 50, bottom: 30, left: 100},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom;
  
var tooltip = d3.select("body").append("div").attr("class", "toolTip");
  
var x = d3.scaleLinear().range([0, width]);
var y = d3.scaleBand().range([height, 0]);
​
var g = svg.append("g")
        .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
  
d3.json("data.json", function(error, data) {
    if (error) throw error;
  
    data.sort(function(a, b) { return a.value - b.value; });
  
    x.domain([0, d3.max(data, function(d) { return d.value; })]);
    y.domain(data.map(function(d) { return d.area; })).padding(0.1);
​
    g.append("g")
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height + ")")
        .call(d3.axisBottom(x).ticks(5).tickFormat(function(d) { return parseInt(d / 1000); }).tickSizeInner([-height]));
​
    g.append("g")
        .attr("class", "y axis")
        .call(d3.axisLeft(y));
​
    g.selectAll(".bar")
        .data(data)
      .enter().append("rect")
        .attr("class", "bar")
        .attr("x", 0)
        .attr("height", y.bandwidth())
        .attr("y", function(d) { return y(d.area); })
        .attr("width", function(d) { return x(d.value); })
        .on("mousemove", function(d){
      // Replace hard coded vals (50, 90) with 50% of the tooltip wioth and height + a top buffer
            tooltip
              .style("left", d3.event.pageX - 50 + "px")
              .style("top", d3.event.pageY - 90 + "px")
              .style("display", "inline-block")
              .html((d.area) + "<br><span>" + "£" + (d.value) + "</span>");
        })
            .on("mouseout", function(d){ tooltip.style("display", "none");});
});
</script>
    