Get max zIndex in NodeList (document)

getMaxZIndex.js

function convertToNumber(value) {
  const asNumber = parseFloat(value);
  return Number.isNaN(asNumber) ? 0 : asNumber;
}

function getNodeZIndex(node) {
  const computedIndex = convertToNumber(window.getComputedStyle(node).zIndex);
  const styleIndex = convertToNumber(node.style.zIndex);

  if (computedIndex > styleIndex) {
    return computedIndex;
  }

  return styleIndex;
}

export function maxZIndex(nodeList) {
  const zIndexes = Array.from(nodeList).map(getNodeZIndex);
  return Math.max(...zIndexes);
}