CSS ルールが存在しない場合に JavaScript で DIV の実際の行の高さを見つける方法

function getLineHeight(el) {
  // Create a temporary element to clone the target element's properties
  const temp = document.createElement(el.nodeName);

  // Override default styles to ensure consistent font properties
  temp.setAttribute("style", "margin:0; padding:0; font-family:" +
    (el.style.fontFamily || "inherit") + "; font-size:" +
    (el.style.fontSize || "inherit"));

  // Set the temporary element's content to "A"
  temp.innerHTML = "A";

  // Append the temporary element to the DOM
  el.parentNode.appendChild(temp);

  // Get the computed height of the temporary element
  const ret = temp.clientHeight;

  // Remove the temporary element
  temp.parentNode.removeChild(temp);

  // Return the computed height, which represents the actual line-height
  return ret;
}