D3 js图像节点间的链接长度

var simulation = d3.forceSimulation(nodes)
    .force("link", d3.forceLink(links).id(function(d) { return d.id; }).distance(100))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));

var simulation = d3.forceSimulation(nodes)
    .force("link", d3.forceLink(links).id(function(d) { return d.id; }).distance(function(d) { return d.distance; }))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));