SOURCE

var nodeData = [
  {name:"aaaa"},
  {name:"bbbb"},
  {name:"ssss"},
  {name:"dddd"}
];
var linkData = [
  {source:0,target:1},
  {source:0,target:2},
  {source:0,target:3},
];
var width = 500;
var height = 300;
var svg = d3.select("#forceMap").append("svg")
.attr("width",width)
.attr("height",height);

var forceGroup = svg.append("g");
var force = d3.layout.force()
.nodes(nodeData)
.links(linkData)
.size([width,height])
.linkDistance(50)
.charge([-150])
.alpha(0);

force.start();
var links = forceGroup.selectAll("line")
.data(linkData)
.enter()
.append("line")
.attr("stroke","#000");
var nodes = forceGroup.selectAll("circle")
.data(nodeData)
.enter()
.append("circle")
.attr("r",5)
.attr("fill",function(d){
  if(d.weight == linkData.length){
    return "red"
  }else{
    return "green"
  }
});



force.on("tick",function(){
  links.attr("x1",function(d){ return d.source.x; })
                        .attr("y1",function(d){ return d.source.y; })
                        .attr("x2",function(d){ return d.target.x; })
                        .attr("y2",function(d){ return d.target.y; });

                    nodes.attr("cx",function(d){ return d.x; })
                        .attr("cy",function(d){ return d.y; });
})

<div id="forceMap">
  
</div>

#forceMap{
  width:500px;
  height:300px;
}