s.matthew.english s.matthew.english - 1 year ago 86
Javascript Question

passing a variable filename to topojson

in the following function is I do this it works:

var land = topojson.feature(europe, europe.objects.nuts1);

but if I do this it breaks:

var europe_path = "europe.objects.nuts1";

var land = topojson.feature(europe, europe_path);

with this error
Uncaught TypeError: Cannot read property 'length' of undefined

how to pass a variable to topojson?

The code looks like this:

.border {
stroke: #000;
fill: none;

.graticule {
fill: none;
stroke: #777;
stroke-width: .5px;
stroke-opacity: .5;

div.tooltip {
position: absolute;
text-align: center;
width: 84px;
height: 64px;
padding: 2px;
font: 12px sans-serif;
background: lightgrey;
border: 0px;
border-radius: 8px;
pointer-events: none;

<h1>Administrative Sub-Regions of Europe</h1>

<select id="json_sources" name="json_sources">
<option value ="nuts1" selected>Source 1</option>
<option value ="nuts2">Source 2</option>
<!-- <option value ="source3.json">Source 3</option> -->

<script src="http://d3js.org/d3.v3.min.js"></script>
<script src="http://d3js.org/topojson.v1.min.js"></script>
<script src="http://d3js.org/colorbrewer.v1.min.js"></script>
<script src="https://cdn.rawgit.com/rveciana/d3-composite-projections/v0.2.0/composite-projections.min.js"></script>

var div = d3.select("body").append("div")
.attr("class", "tooltip")
.style("opacity", 0);

var width = 600,
height = 500;

var projection = d3.geo.conicConformalEurope();
var graticule = d3.geo.graticule();

var path = d3.geo.path()

// Find new colours here: http://colorbrewer2.org/
var scale = d3.scale.quantize().domain([10,60]).range(colorbrewer.PuRd[3]);
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height);

.attr("class", "graticule")
.attr("d", path);

var dropdown = d3.select("#json_sources")
var change = function() {
var source = dropdown.node().options[dropdown.node().selectedIndex].value;

var str1 = source;
var str2 = ".json";
var file = str1.concat(str2);

var str_a = "europe.objects.";
var str_b = source;
var europe_path = str_a.concat(str_b);

d3.json(file, function(error, europe) {

d3.csv("povertry_rate.csv", function(error, povrate) {

var europe_path = "europe.objects.nuts1";

var land = topojson.feature(europe, europe_path);

data = {};
povrate.forEach(function(d) {
data[d.GEO] = d['2013'];

.attr("d", path)
var value = data[d.id];
if (isNaN(value)){
value = data[d.id.substring(0,2)];
if (isNaN(value)){
return "#fff";

return scale(value);
.on("mouseover", function(d,i) {
var value = data[d.id];
if (isNaN(value)){
value = data[d.id.substring(0,2)];
.style("opacity", 0.9);
div.html("<b>"+d.properties.name+"</b><br/>" + value + "%")
.style("left", (d3.event.pageX) + "px")
.style("top", (d3.event.pageY - 28) + "px");
.on("mouseout", function(d,i) {
.style("opacity", 0);

.attr("d", projection.getCompositionBorders());



dropdown.on("change", change)
change(); //trigger json on load



<!-- // d3.json("nuts2.json", function(error, europe) {

// }); -->

Answer Source

You are defining europe_path as a string "europe.object.nuts1" rather than the object europe.object.nuts1. Remove the quotations and try it.

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