D3 chart with JSON web service - json

Question

I am trying to make the following bar chart from this tutorial. The tutorial utilizes TSV files, but I have modified the code for JSON. I have checked that the endpoint http://localhost:3000/graphs/data from my Node / Express service I created is indeed returning JSON, which can be seen below. The proper D3 libraries are also being included. After checking all this, I cannot get the chart to render.
The goal is to have route on the x-axis and count on the y-axis. Any suggestions would be greatly appreciated.
JSON Response:
[{"route":"9","count":273},{"route":"49","count":242},{"route":"151","count":221},{"route":"8","count":220},{"route":"3","count":213},{"route":"82","count":209},{"route":"79","count":206},{"route":"N5","count":206},{"route":"62","count":206},{"route":"4","count":202}]
Bar Chart Code
<script>
var margin = {top: 40, right: 20, bottom: 30, left: 40},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
var formatPercent = d3.format(".0%");
var x = d3.scale.ordinal()
.rangeRoundBands([0, width], .1);
var y = d3.scale.linear()
.range([height, 0]);
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom");
var yAxis = d3.svg.axis()
.scale(y)
.orient("left");
var tip = d3.tip()
.attr('class', 'd3-tip')
.offset([-10, 0])
.html(function(d) {
return "<strong>Count:</strong> <span style='color:red'>" + d.count + "</span>";
})
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.call(tip);
d3.json('http://localhost:3000/graphs/data', type, function(error, data) {
x.domain(data.map(function(d) { return d.route; }));
y.domain([0, d3.max(data, function(d) { return d.count; })]);
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
svg.append("g")
.attr("class", "y axis")
.call(yAxis)
.append("text")
.attr("transform", "rotate(-90)")
.attr("y", 6)
.attr("dy", ".71em")
.style("text-anchor", "end")
.text("Frequency");
svg.selectAll(".bar")
.data(data)
.enter().append("rect")
.attr("class", "bar")
.attr("x", function(d) { return x(d.route); })
.attr("width", x.rangeBand())
.attr("y", function(d) { return y(d.count); })
.attr("height", function(d) { return height - y(d.count); })
.on('mouseover', tip.show)
.on('mouseout', tip.hide)
});
function type(d) {
d.count = +d.count;
return d;
}
</script>

Answer 1

d3.json(), unlike d3.csv(), takes only two arguments, with the second being the callback function. Your call
d3.json('http://localhost:3000/graphs/data', type, function(error, data) {
passes the result of the call to type, not to the anonymous function after that, which is never executed. The call should be
d3.json('http://localhost:3000/graphs/data', function(error, data) {