function for crossfade transition of text using d3 based on this block: https://bl.ocks.org/mbostock/f7dcecb19c4af317e464

text_transistion.js

        function transition_text(element_id, display_text, t_duration){
          // base off of https://bl.ocks.org/mbostock/f7dcecb19c4af317e464
          svg.select(element_id)
              .transition()
              .duration(t_duration)
              .on("start", function () {
                  var t = d3.active(this)
                      .style("opacity", 0)
                      .remove();

                  svg.select(element_id)
                      .style("opacity", 0)
                      .text(display_text)
                      .transition(t)
                      .style("opacity", 1)
                      .transition()
              });
        }