Adding 'rect' elements to blank svg canvas in d3 is failing on .data()

Question

I'm using Polymer to render some d3 charts. When the Polymer is initially rendered I only draw a graph with axes and no data, since the data comes later once the API calls succeed. However, when I get around to selecting the 'rect' elements in the svg, calling data() on that fails. Here's my code:

dataChanged: function() {
    var data = this.data;
    var margin = {top: 20, right: 20, bottom: 30, left: 50},
        width = this.width - margin.left - margin.right,
        height = this.height - margin.top - margin.bottom;

      // format the data
    data.forEach(function(d) {
        d.date = d3.isoParse(d.date);
    });

    // set the ranges
    var x = d3.scaleTime()
        .domain(d3.extent(data, function(d) { return d.date; }))
        .rangeRound([0, width]);
    var y = d3.scaleLinear()
        .range([height, 0]);

    var svg = d3.select(this.$.chart).transition();

    var histogram = d3.histogram()
        .value(function(d) { return d.date; })
        .domain(x.domain())
        .thresholds(x.ticks(d3.timeMonth));

    var bins = histogram(data);

    y.domain([0, d3.max(bins, function(d) { return d.length; })]);

    svg.selectAll("rect")
        .data(bins)
        .enter().append("rect")
        .attr("class", "bar")
        .attr("x", 1)
        .attr("transform", function(d) {
          return "translate(" + x(d.x0) + "," + y(d.length) + ")";
        })
        .attr("width", function(d) { return x(d.x1) - x(d.x0) -1 ; })
        .attr("height", function(d) { return height - y(d.length); });

    svg.select(".xAxis")
        .duration(300)
        .call(d3.axisBottom(x));

    svg.select(".yAxis")
        .duration(300)
        .call(d3.axisLeft(y));
},
ready: function() {
    var margin = {top: 20, right: 20, bottom: 30, left: 50},
        width = this.width - margin.left - margin.right,
        height = this.height - margin.top - margin.bottom;

    // set the ranges
    var x = d3.scaleTime()
        .domain([new Date(2010, 6, 3), new Date(2012, 0, 1)])
        .rangeRound([0, width]);
    var y = d3.scaleLinear()
        .range([height, 0]);

    // Add the SVG to my 'chart' div.    
    var svg = d3.select(this.$.chart).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 + ")");

    // Add the X Axis
    svg.append("g")
        .attr("class","xAxis")
        .attr("transform", "translate(0," + height + ")")
        .call(d3.axisBottom(x));

    // Add the Y Axis
    svg.append("g")
        .attr("class","yAxis")
        .call(d3.axisLeft(y));
 }

ready() gets called upon rendering, dataChanged() when the parent component passes a chunk of data down. Everything works fine until svg.selectAll("rect").data(bins) is called when it crashes with Uncaught TypeError: svg.selectAll(...).data is not a function . bins has the right data in it, so that's not empty. I know that there are no rect elements for it to select, but in the example I followed here there are no rect elements prior to them being appended by this call anyway, so I'm confused as to why this doesn't work.

Answer 1

What's the purpose of this line:

var svg = d3.select(this.$.chart).transition();

This would make svg a transition, your code is implying it should be selection. So, just drop it the .transition :

var svg = d3.select(this.$.chart);

...

svg.selectAll("rect")
  .data(bins)
  ...