javascript - D3.js tree with odd number of vertices, edges not shown

Question

I have the following JavaScript code that uses the D3.js library to draw a tree (it follows the standard structure one can find in the various online tutorials):

var json = {
    "name": "A",
        "children": [{
        "name": "B"
    }]
};

var tree = d3.layout.tree().size([200, 200]);

var nodes = tree.nodes(json);

var vis = d3.select("#chart").attr("width", 300)
    .attr("height", 300)
    .append("svg:g")
    .attr("transform", "translate(40, 40)");

var diagonal = d3.svg.diagonal();

var link = vis.selectAll("path.link").data(tree.links(nodes)).enter()
    .append("svg:path")
    .attr("class", "link")
    .attr("d", diagonal);

var node = vis.selectAll("g.node").data(nodes).enter().append("svg:g")
    .attr("class", "node")
    .attr("transform", function (d) {
    return "translate(" + d.x + "," + d.y + ")";
});

node.append("svg:circle").attr("r", 10);

node.append("svg:text").attr("dx", function (d) {
    return 10;
})
    .attr("dy", 10)
    .attr("text-anchor", function (d) {
    return "start";
})
    .text(function (d) {
    return d.name;
});

JSFIDDLE

It works mostly fine, except for trees in which a vertex has an odd number of children (1, 3, ...); in this case, the edge for the odd vertex will not be drawn (e.g., in the above example, the edge between A and B is not displayed). What am I missing?

Answer 1

You are missing the style for the node links. Something variation of this:

<style>
.link {
    fill: none;
    stroke: #ccc;
    stroke-width: 4.5px;
}
</style>

Or, set it on the link itself:

.attr("d", diagonal).attr({ 'fill': 'none', 'stroke': 'grey', 'stroke-width': 4 });

It depends on odd vs. even number because by default a path gets no stroke and a fill color of black. So a straight line doesn't show up but the curved ones get filled.