Moove objects Above other objects

d3-plugins.js

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

d3.selection.prototype.moveToBack = function() { 
    return this.each(function() { 
        var firstChild = this.parentNode.firstChild; 
        if (firstChild) { 
            this.parentNode.insertBefore(this, firstChild); 
        } 
    }); 
};


// Usage example
circles.on("mouseover",function(){
  var sel = d3.select(this);
  sel.moveToFront();
});