Click-to-Recenter Brush II

A variation of the click-to-recenter brush with snapping on brushend.

<!DOCTYPE html>
<style>

.selected {
  fill: red;
  stroke: brown;
}

</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var randomX = d3.randomUniform(0, 10),
    randomY = d3.randomNormal(0.5, 0.12),
    data = d3.range(800).map(function() { return [randomX(), randomY()]; });

var svg = d3.select("svg"),
    margin = {top: 194, right: 50, bottom: 214, left: 50},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom,
    g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var x = d3.scaleLinear()
    .domain([0, 10])
    .range([0, width]);

var y = d3.scaleLinear()
    .range([height, 0]);

var brush = d3.brushX()
    .extent([[0, 0], [width, height]])
    .on("start brush", brushed)
    .on("end", brushended);

var dot = g.append("g")
    .attr("fill-opacity", 0.2)
  .selectAll("circle")
  .data(data)
  .enter().append("circle")
    .attr("transform", function(d) { return "translate(" + x(d[0]) + "," + y(d[1]) + ")"; })
    .attr("r", 3.5);

g.append("g")
    .call(brush)
    .call(brush.move, [3, 5].map(x))
  .selectAll(".overlay")
    .each(function(d) { d.type = "selection"; }) // Treat overlay interaction as move.
    .on("mousedown touchstart", brushcentered); // Recenter before brushing.

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

function brushcentered() {
  var dx = x(1) - x(0), // Use a fixed width when recentering.
      cx = d3.mouse(this)[0],
      x0 = cx - dx / 2,
      x1 = cx + dx / 2;
  d3.select(this.parentNode).call(brush.move, x1 > width ? [width - dx, width] : x0 < 0 ? [0, dx] : [x0, x1]);
}

function brushed() {
  if (!d3.event.selection) return; // Ignore empty selections.
  var extent = d3.event.selection.map(x.invert, x);
  dot.classed("selected", function(d) { return extent[0] <= d[0] && d[0] <= extent[1]; });
}

function brushended() {
  if (!d3.event.sourceEvent) return; // Only transition after input.
  if (!d3.event.selection) return; // Ignore empty selections.
  var d0 = d3.event.selection.map(x.invert),
      d1 = d0.map(Math.round);

// If empty when rounded, use floor & offset instead.
  if (d1[0] >= d1[1]) {
    d1[0] = Math.floor(d0[0]);
    d1[1] = d1[0] + 1;
  }

d3.select(this).transition().call(brush.move, d1.map(x));
}

</script>

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