d3.js: “Cannot read property 'weight' of undefined” when manually defining both nodes and links for force layout

Question

I tried setting both nodes and links at the same time this way:

var force = d3.layout.force()
    .size([w, h])
    .nodes(nodes)
    .links(connections)
            


        

Answer 1

Thanks to the answers above which refer to null source or target values!

I've been testing out the graph from http://bl.ocks.org/mbostock/4062045, and found that my data referenced a missing node.

This may help others debug this issue:

d3.json("my-buggy-data.json", function(error, graph) {

    // Find blank links, which give the error
    // "Uncaught TypeError: Cannot read property 'weight' of undefined"
    graph.links.forEach(function(link, index, list) {
        if (typeof graph.nodes[link.source] === 'undefined') {
            console.log('undefined source', link);
        }
        if (typeof graph.nodes[link.target] === 'undefined') {
            console.log('undefined target', link);
        }
    });

    force
        .nodes(graph.nodes)
        .links(graph.links)
        .start();