Transitioning hacking with clock manipulation

Transition hacking by overwriting Date.now, tricking d3.timer into thinking it's whatever time we want. Beyond the obvious red flags of overwriting a browser global, this only really works for moving forward (each transition in a chain self-deletes once it hits t=1). I would not recommend this.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  text-align: center;
  font: 16px sans-serif;
}

button {
  margin: 0 0.5em;
}

circle {
  stroke: #000;
  stroke-width: 1.5px;
}

</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.16/d3.min.js"></script>
<script>

var margin = {top: 100, right: 100, bottom: 100, left: 100},
    width = 960 - margin.left - margin.right,
    height = 440 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
    .domain(d3.range(5))
    .rangePoints([0, width]);

var y = x.copy()
    .rangePoints([0, height]);

var color = d3.scale.linear()
    .domain(d3.extent(x.domain()))
    .range(["hsl(297,50%,47%)", "hsl(81,78%,61%)"])
    .interpolate(d3.interpolateHcl);

var svg = d3.select("body").append("svg")
  .attr("width", width + margin.left + margin.right)
  .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var dots = svg.selectAll("circle")
  .data(x.domain())
  .enter()
  .append("circle")
    .attr("r",20)
    .attr("cx",0)
    .attr("cy",y)
    .style("fill",color);

var curTime = 0,
    _now = Date.now; // save for later

// FREEZE TIME
Date.now = function fakeNow(){
  return curTime;
};

// Create a transition
dots.transition()
  .duration(3500)
  .delay(function(d){
    return d * 125;
  })
  .attr("cx",x)
  .attr("r",40)
  .transition()
    .duration(2000)
    .attr("r",20)
    .attr("cx",width);

d3.select("body").append("div")
  .text("Jump to: ")
  .selectAll("button")
  .data(d3.range(0,6500,500))
  .enter()
  .append("button")
    .text(function(d){
      return (Math.round(d/100)/10) + " s";
    })
    .on("click",function(d){
      curTime = d; // TIME TRAVEL
    });

d3.select("div").append("button")
  .text("Finish")
  .style("font-weight","bold")
  .on("click",function(){

d3.selectAll("button").attr("disabled",true).on("click",null);

var now = _now();

d3.timer(function(){

var t = _now();

curTime += (t - now);
      now = t;

if (curTime >= 6000) {
        // Transitions are all done
        // Restore REAL TIME
        Date.now = _now;
        d3.select("div").remove();
        return true;
      }
    },0,0);

});

</script>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.16/d3.min.js