JSFiddle - React, Tailwind, and code Playground

HTML

<button>Randomize</button>
<svg xmnls="http://www.w3.org/2000/svg">
  <path id="example" d="M10 10 C 20 20, 40 20, 50 10" />
  <circle r="5" cx="0" cy="0" id="minX" />
  <circle r="5" cx="0" cy="0" id="minY" />
  <circle r="5" cx="0" cy="0" id="maxX" />
  <circle r="5" cx="0" cy="0" id="maxY" />
</svg>

CSS

svg {
  position: absolute;
  height: 100%;
  width: 100%;
  display: block;
}

path {
  fill: none;
  stroke-width: 5;
  stroke: black;
}

circle {
  fill: red;
}

JavaScript

var example = document.getElementById("example");
var button = document.querySelector("button");
var svg = document.querySelector("svg");
button.addEventListener("click", randomize);


var dimensions= {
   width: window.innerWidth,
   height: window.innerHeight
}


randomize();

function randomize(){
  var w = dimensions.width;
  var h = dimensions.height;
  var r = function(dim) {return Math.random() * dim};
  example.setAttribute("d", "M" + r(w) + " " + r(h) + " C " + r(w) + " " + r(h) + ", " + r(w) + " " + r(h) + ", " + r(w) + " " + r(h))
  drawLimits(findLimits(example));
}

function findLimits(path) {

  var boundingPoints = {
    minX: {x: dimensions.width, y: dimensions.height},
    minY: {x: dimensions.width, y: dimensions.height},
    maxX: {x: 0, y: 0},
    maxY: {x: 0, y: 0}
  }
  var l = path.getTotalLength();
  for (var p = 0; p < l; p++) {
  	var coords = path.getPointAtLength(p);
    if (coords.x < boundingPoints.minX.x) boundingPoints.minX = coords;
    if (coords.y < boundingPoints.minY.y) boundingPoints.minY = coords;
    if (coords.x > boundingPoints.maxX.x) boundingPoints.maxX = coords;
    if (coords.y > boundingPoints.maxY.y) boundingPoints.maxY = coords;
  }
  return boundingPoints
}

function drawLimits(boundingPoints){
  ["minX", "minY", "maxX", "maxY"].forEach(function(point){
    var circle = svg.getElementById(point);
    console.log(circle)
    circle.setAttribute("cx", boundingPoints[point].x);
    circle.setAttribute("cy", boundingPoints[point].y);
  })
}