title: D3 v4 xAxis zoom return x as NaN making rescale(x) unable to complete
body: <p>I'm trying to achieve an zoom option with x axis as date format.
  Here's the code sample:</p>
  
  <pre><code>var margin = {
  top: 20,
  right: 20,
  bottom: 40,
  left: 100
    },
    svgWidth = 800,
    svgHeight = 500,
    width = svgWidth - margin.left - margin.right,
    height = svgHeight - margin.top - margin.bottom;
  
  svg = d3.select('body')
    .append("svg")
    .attr("style", "width: " + svgWidth + "px\; height: " + svgHeight + "px\;");
  
  var x = d3.scaleUtc().range([0, width])
    .domain([new Date("3/12/2017"), new Date("3/30/2017")]);
  
  var y = d3.scaleBand()
    .range([height, 0])
    .padding(0.1)
    .domain(["test"])
  
  var xAxis = d3.axisBottom(x)
    .tickFormat(d3.utcFormat("%m-%d"));
  
  var yAxis = d3.axisLeft(y);
  
  var zoom = d3.zoom()
    .scaleExtent([1, Infinity])
    .translateExtent([0, 0], [width, height])
    .extent([[0, 0], [width, height]])
    .on("zoom", zoomed);
  
  var xLine = svg.append("g")
    .attr("transform", "translate(" + margin.left + "," + height + ")")
    .attr("class", "xAxis")
    .call(xAxis)
    .selectAll("text")
    .style("text-anchor", "middle");
  var yLine = svg.append("g")
    .attr("transform", "translate(" + margin.left + ", 0)")
    .attr("class", "yAxis")
    .call(yAxis)
    .selectAll("text")
    .attr("class", "cateName")
    .style("text-anchor", "end");
  
  svg.call(zoom);
  
  function zoomed() {
    xLine.call(xAxis.scale(d3.event.transform.rescaleX(x)));
  };
  </code></pre>
  
  <p>The idea is very simple, when you pan horizontally, the xAxis will adjust the position. However, when you click the SVG, all labels in x axis will disappear.
  I tried to look into it but it seems that my <code>x</code> in <a href="https://github.com/d3/d3-zoom/blob/master/src/transform.js#L13" rel="nofollow noreferrer">source code</a> is <code>NaN</code>.</p>
  
  <p>Why is this happening? Am I missing something?
  The JSFiddle is here: <a href="https://jsfiddle.net/amyytnt0/1/" rel="nofollow noreferrer">https://jsfiddle.net/amyytnt0/1/</a></p>
  
  <p>Thanks for your help!</p>