Inner and outer ticks on an axis

<!DOCTYPE html>
<meta charset="utf-8">
<head>
  <style>
 
  body {
    font: 10px sans-serif;
  }
 
  .axis path, .axis line {
    fill: none;
    stroke: #000;
    shape-rendering: crispEdges;
  }

</style>

</head>

<body>
  <div id="chart"></div>
  <p>An example of verticle lines extending from an x using innerTickSize and outerTickSize</p>
</body>

var margin = {top: 10, right: 30, bottom: 30, left: 30},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;
 
var x = d3.scale.linear()
    .domain([0, 25])
    .range([0, width]);
 
var data = [1, 2, 3, 5, 8, 13, 21];

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("top")
    .tickValues(data)
    .innerTickSize([250])
    .outerTickSize([250]);
 
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
 
svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis);
 
</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js