Axis Styling II by mbostock

This example demonstrates the use of post-selection to customize an axis during transitions. After the axis is rendered, its elements (such as text labels, here) are reselected and modified to produce the desired appearance. When transitioning the axis, the post-selection modifies entering, updating and exiting elements. Passing null values to transition.tween cancels default tweens scheduled by the axis in favor of the customized styles.

index.html

<!DOCTYPE html>
<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: 0, bottom: 20, left: 0},
    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 formatNumber = d3.format(".1f");

var x = d3.scaleTime()
    .domain([new Date(2010, 7, 1), new Date(2012, 7, 1)])
    .range([0, width]);

var y = d3.scaleLinear()
    .domain([0, 2e6])
    .range([height, 0]);

var xAxis = d3.axisBottom(x)
    .ticks(d3.timeYear);

var yAxis = d3.axisRight(y)
    .tickSize(width)
    .tickFormat(function(d) {
      var s = formatNumber(d / 1e6);
      return this.parentNode.nextSibling
          ? "\xa0" + s
          : "$" + s + " million";
    });

var xGroup = g.append("g")
    .attr("transform", "translate(0," + height + ")")
    .call(customXAxis);

var yGroup = g.append("g")
    .call(customYAxis);

d3.timeout(function() {
  y.domain([0, 4e6]);
  yGroup.transition().duration(2500).call(customYAxis);
}, 1000);

function customXAxis(g) {
  g.call(xAxis);
  g.select(".domain").remove();
}

function customYAxis(g) {
  var s = g.selection ? g.selection() : g;
  g.call(yAxis);
  s.select(".domain").remove();
  s.selectAll(".tick line").filter(Number).attr("stroke", "#777").attr("stroke-dasharray", "2,2");
  s.selectAll(".tick text").attr("x", 4).attr("dy", -4);
  if (s !== g) g.selectAll(".tick text").attrTween("x", null).attrTween("dy", null);
}

</script>