在下面的函数中，我这样做是有效的:
var land = topojson.feature(europe, europe.objects.nuts1);
但如果我这样做，它就会崩溃:
var europe_path = "europe.objects.nuts1";
var land = topojson.feature(europe, europe_path);
出现此错误 Uncaught TypeError: Cannot read property 'length' of undefined
如何将变量传递给topojson？
代码如下:
.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;
}
</style>
<body>
<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> -->
</select>
<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>
<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()
.projection(projection);
// 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);
svg.append("path")
.datum(graticule)
.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);
console.log(file);
var str_a = "europe.objects.";
var str_b = source;
var europe_path = str_a.concat(str_b);
console.log(europe_path);
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'];
});
console.info(data);
svg.selectAll("path")
.data(land.features)
.enter()
.append("path")
.attr("d", path)
.style("stroke","#000")
.style("stroke-width",".5px")
.style("fill",function(d){
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)];
}
div.transition()
.duration(200)
.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) {
div.transition()
.duration(500)
.style("opacity", 0);
});
svg
.append("path")
.style("fill","none")
.style("stroke","#000")
.attr("d", projection.getCompositionBorders());
});
})
}
dropdown.on("change", change)
change(); //trigger json on load
</script>
</body>
<!-- // d3.json("nuts2.json", function(error, europe) {
// }); -->
最佳答案
您将 europe_path 定义为字符串“europe.object.nuts1”而不是对象 europe.object.nuts1。删除引号并尝试。
编辑开始****
如果目标是允许用户在两层之间切换，您可以使用变量名动态加载 topojson，例如:
Toggle Topojson with file reload
采用与所提供代码类似的方法。
但是，如果目标是允许在两个或更多层之间切换，加载它们一次并切换可见性可能会更容易，如:
Toggle Topojson with visibility change
这通常会更顺畅和更快，因为不需要从重新加载的 topojson 文件重新计算路径。
编辑结束****
关于javascript - 将变量文件名传递给 topojson，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/40454843/