D3: Callback when all elements have transitioned

example.js

var features = d3.selectAll("path")

features.transition().ease("quad-in-out").duration(1000)
    .attr("d",path.pointRadius(set_circle_radius))
    .style("fill", set_circle_color)
    // call the helper function passing the desired callback function
    .call(d3endall, enable_map_events);
    
//Helper counting function to wait to all elements of a transition to end
function d3endall(transition, callback) { 
    if (transition.size() === 0) { callback(); }
    var n = 0; 
    transition 
        .each(function() { ++n; }) 
        .each("end", function() { if (!--n) callback.apply(this, arguments); }); 
}

function enable_map_events () {
  // Enable drag and zoom handlers.
  map.dragging.enable();
  map.touchZoom.enable();
  map.doubleClickZoom.enable();
  map.scrollWheelZoom.enable();

  // Enable tap handler, if present.
  if (map.tap) map.tap.enable();
  
}