ease delay

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <script>
 		console.clear()   
    
    
    function delayEase(t, e) {
      	// the polyInOut function from d3.ease
      	// https://github.com/d3/d3-ease/blob/master/src/poly.js
        return ((t *= 2) <= 1 ? Math.pow(t, e) : 2 - Math.pow(2 - t, e)) / 2;
      }
    
		let exp = 0.5 // see https://github.com/d3/d3-ease/blob/master/src/poly.js#L27
    
    let arr = [0,1,2,3,4,5,6,7]
    let len = arr.length
    
    let svg = d3.select("body").append("svg")
    	.attr("width", 1000)
    	.attr("height", 500)
    
    let circles = svg.selectAll("circle")
    	.data(arr)
    	.enter()
    	.append("circle")
    	.attr("cx", d => (d * 40) + 40)
    	.attr("cy", 50)
    	.attr("r", 10)
    	.style("fill", "black")
    
    circles.transition()
    	.duration(5000)
      .delay(function(d,i) {
      	let delay = 5000 * (delayEase((i/len), exp))
        console.log(delay)
      	return delay
    	})
    	.attr("cy", 450)

</script>
</body>

https://d3js.org/d3.v4.min.js