move element to front on mouseover in d3

_.md

[ Launch Inlet ]

config.json

{"endpoint":"","display":"svg","public":true,"require":[],"tab":"edit","display_percent":0.7,"play":false,"loop":false,"restart":false,"autoinit":true,"pause":true,"loop_type":"period","bv":false,"nclones":15,"clone_opacity":0.4,"duration":3000,"ease":"linear","dt":0.01}

inlet.js

d3.selection.prototype.moveToFront = function() {
  return this.each(function(){
  this.parentNode.appendChild(this);
  });
};

var svg = d3.select("svg");

var data = d3.range(10);

var circles = svg.selectAll("circle")
    .data(data)
    .enter()
    .append("circle")
    .attr({
      cx: function(d,i){return d*20+100},
      cy: 100,
      r:20,
      fill:"#aaa",
      stroke: "#000"
    })
    .on("mouseover",function(){
      var sel = d3.select(this);
      sel.moveToFront();
    });