Bar Chart with Tooltip with Tooltip D3 V4

This chart is based on mbostock's block: Bar Chart.

it uses a json file storing area names and average house prices. The chart employs conventional margins and a number of D3 features:

d3.json - load and parse data
d3.tickFormat - format y axis tick text
d3.scale.ordinal - x-position encoding
d3.scale.linear - y-position encoding
d3.max - compute domains
d3.svg.axis - display axes

<!DOCTYPE html>
<meta charset="utf-8">
<style>
body {
  background-color: #F1F3F3    
}
.axis {
	font: 15px sans-serif;
}
.axis path,
.axis line {
  fill: none;
  stroke: #D4D8DA;
  stroke-width: 1px;
  shape-rendering: crispEdges;
}
.toolTip {
  position: absolute;
  display: none;
  min-width: 80px;
  height: auto;
  background: none repeat scroll 0 0 #ffffff;
  border: 1px solid #6F257F;
  padding: 14px;
  text-align: center;
}
</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>

var x = d3.scaleBand().rangeRound([0, width]).padding(0.1),
    y = d3.scaleLinear().rangeRound([height, 0]);
  
var colours = d3.scaleOrdinal()
    .range(["#6F257F", "#CA0D59"]);

var g = svg.append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

d3.json("data.json", function(error, data) {
    if (error) throw error;

x.domain(data.map(function(d) { return d.area; }));
    y.domain([0, d3.max(data, function(d) { return d.value; })]);

g.append("g")
        .attr("class", "axis axis--x")
        .attr("transform", "translate(0," + height + ")")
        .call(d3.axisBottom(x));

g.append("g")
      	.attr("class", "axis axis--y")
      	.call(d3.axisLeft(y).ticks(5).tickFormat(function(d) { return parseInt(d / 1000) + "K"; }).tickSizeInner([-width]))
      .append("text")
        .attr("transform", "rotate(-90)")
        .attr("y", 6)
        .attr("dy", "0.71em")
        .attr("text-anchor", "end")
        .attr("fill", "#5D6971")
        .text("Average House Price - (£)");

g.selectAll(".bar")
      	.data(data)
      .enter().append("rect")
        .attr("x", function(d) { return x(d.area); })
        .attr("y", function(d) { return y(d.value); })
        .attr("width", x.bandwidth())
        .attr("height", function(d) { return height - y(d.value); })
        .attr("fill", function(d) { return colours(d.area); })
        .on("mousemove", function(d){
            tooltip
              .style("left", d3.event.pageX - 50 + "px")
              .style("top", d3.event.pageY - 70 + "px")
              .style("display", "inline-block")
              .html((d.area) + "<br>" + "£" + (d.value));
        })
    		.on("mouseout", function(d){ tooltip.style("display", "none");});
    });
</script>

https://d3js.org/d3.v4.min.js