Fn to create dots when clicking an element, Fn helper to convert these to scaled, compact array

onClickMakeDots.js

/* const */ dotsMadeStoreArr = [];

function attachOnClickMakeDotsListener(elm) {
  function onClickMakeDotsListener(evt) {
    onClickMakeDots(evt);
  }
  elm.addEventListener("click", onClickMakeDotsListener);

  return function detachOnClickMakeDotsListener() {
    elm.removeEventListener("click", onClickMakeDotsListener);
  }
}

function onClickMakeDots(e) {
  const x = e.offsetX / e.target.offsetWidth;
  const y = e.offsetY / e.target.offsetHeight;
  if (dotsMadeStoreArr != null && dotsMadeStoreArr instanceof Array) {
    dotsMadeStoreArr.push([x,y])
  }
    
  const elm = document.createElement("div")
  elm.style.position = "absolute"
  elm.style.width = "4px"
  elm.style.height = "4px"
  elm.style.backgroundColor = "red";
  elm.style.borderRadius = "20px";

  elm.style.left = (x * 100).toFixed(4) + "%";
  elm.style.top =  (y * 100).toFixed(4) + "%";
  console.log(`Created Dot at left=${elm.style.left} top=${elm.style.top}`)

  e.target.appendChild(elm);
}


/**
 * getScale
 * Creates an scaling function based on two ranges
 *
 * @param from [number, number] : the domain of the value you will pass as input
 * @param to [number, number] : the corresponding range it should output
 * @returns (number) => number : the scaling function
 */
function getScale(from, to) {
  return function _scale(value) {
    return (value - from[0]) * (to[1] - to[0]) / (from[1] - from[0]) + to[0];
  }
}

/**
 * tupleToString
 * Receive an number tuple, scale, parse decimals and return it as compact string
 *
 * @param tupleArr Array : like [ [number, number], [number, number] ]
 * @param decimals number : how many decimals to keep (default 0)
 * @param scaleFn (number) => number : function to transform the values
 * @returns String : should look like "[[-4,8],[15,16],[23,42]]"
 */
function tupleToString(tupleArr, decimals = 0, scaleFn = (x) => x) {
  return '[' + tupleArr
    .map((x) => [
      scaleFn(x[0]).toFixed(decimals),
      scaleFn(x[1]).toFixed(decimals),
    ])
    .map(x => `[${x[0]},${x[1]}]`)
    .join(',')
    + ']';
}