How to apply individual parameters to easing in transitions?

I make a transition to objects like

.transition()
.duration(600)
.delay(function(d, i) { return (500 - (i * 40)); })
.ease(d3.easeBackInOut)

In the documentation there are different parameters possible to manipulate the type of easing like backInOut(t, 3.0) but I do not know how to apply t and a different amplitude... Any help on that?

https://github.com/d3/d3-ease#easeBackInOut

Solution

In the specific case of d3.easeBackInOut you can set the amplitude (called overshoot in the API) by using overshoot():

.ease(d3.easeBackInOut.overshoot(s))
//your value here----------------^

Here is a demo using 3 as the overshoot (the default value is 1.70158):

const svg = d3.select("svg");
svg.append("circle")
  .attr("cx", 100)
  .attr("cy", 50)
  .attr("r", 10)
  .style("stroke", "black")
  .style("fill", "lightgray")
  .transition()
  .duration(2000)
  .ease(d3.easeBackInOut.overshoot(3))
  .attr("cx", 400);

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"></script>
<svg width="500" height="100"></svg>

By the way, you don't need to mess with t. Its value, going from 0 to 1, is automatically passed to the easing function.