d3 fitextent and responsive projection

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
  body {
    margin: 0;
  }
  svg {
    fill: steelblue;
  }
  </style>
</head>
<body>
  <svg></svg>
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <script src="https://d3js.org/topojson.v1.min.js"></script>
  <script>

var width = document.documentElement.clientWidth,
      height = width / 2,
      svg = d3.select("svg").attr('width', width).attr('height', height),
      path,
      counties;

d3.json("ok-counties.json", function(error, ok) {
    if (error) throw error;

counties = topojson.feature(ok, ok.objects.counties);

path = d3.geoPath()
        .projection(d3.geoMercator()
          .fitSize([width, height], counties));

svg.append("path")
        .datum(counties)
        .attr("d", path);
  });

var optimizedResize = (function() {

var callbacks = [],
          running = false;

// fired on resize event
      function resize() {

if (!running) {
              running = true;

if (window.requestAnimationFrame) {
                  window.requestAnimationFrame(runCallbacks);
              } else {
                  setTimeout(runCallbacks, 66);
              }
          }

}

// run the actual callbacks
      function runCallbacks() {

callbacks.forEach(function(callback) {
              callback();
          });

running = false;
      }

// adds callback to loop
      function addCallback(callback) {

if (callback) {
              callbacks.push(callback);
          }

}

return {
          // public method to add additional callback
          add: function(callback) {
              if (!callbacks.length) {
                  window.addEventListener('resize', resize);
              }
              addCallback(callback);
          }
      };
  }());

// start process
  optimizedResize.add(function() {

width = document.documentElement.clientWidth;
    height = width / 2;
    svg.attr('width', width).attr('height', height);

path.projection(d3.geoMercator()
      .fitSize([width, height], counties));

d3.select('path').attr('d', path);
  });

</script>
</body>
</html>

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

https://d3js.org/topojson.v1.min.js