Unable to get click event in D3 JavaScript library

Try out this, if you want the node contained within the circle (let's say that your nodes are mapping an object with a key called anger and a value 34:

var circle = svg.append("svg:g").selectAll("circle")
.data(force.nodes())
.enter().append("svg:circle")
.attr("r", 6)
.on("click", function(d,i) { alert(d.anger); }) // this will alert 34
.call(force.drag);

Or try this for the attributes of the svg (getting the radius of the svg, for example):

var circle = svg.append("svg:g").selectAll("circle")
.data(force.nodes())
.enter().append("svg:circle")
.attr("r", 6)
.on("click", function(d,i) { alert(d3.select(this).r; }) // this will print out the radius })
.call(force.drag);

Sorry if my post is like the one above, but I thought the clarification could be useful.

Try this:

var circle = svg.append("svg:g").selectAll("circle")
  .data(force.nodes())
  .enter().append("svg:circle")
  .attr("r", 6)
  .on("click", function(d,i) { alert("Hello world"); })
  .call(force.drag);