Easier syntax for looped transitions?

[mbostock]

This isn’t a particularly constructive comment, but I’m writing it down anyway. I find the syntax for chained transitions to be difficult to remember, e.g.,

selection.transition()
    .duration(2500)
    .delay(function(d) { return d * 40; })
    .each(slide);

function slide() {
  var circle = d3.select(this);
  (function repeat() {
    circle = circle.transition()
        .attr("cx", width)
      .transition()
        .attr("cx", 0)
        .each("end", repeat);
  })();
}

First you have a selection, then an initial transition, but then you call transition.each to create a selection again, before using a self-executing closure that overwrites itself, and circle is initially a selection but then later a transition… blech.

[mbostock]

d3-transition adds d3.active, so this is much easier in D3 4.0.