How to Find the Actual Line-Height of a DIV in JavaScript When No CSS Rule Exists?

Finding the Actual Line-Height of a DIV in JavaScript

In JavaScript, obtaining the line-height of an element is straightforward through the style.lineHeight property. However, this approach relies on the existence of a CSS style rule specifying the line-height. When such a rule is absent, determining the actual rendered line-height of an element poses a different challenge.

The Solution: Utilizing ClientHeight

The actual line-height can be accurately determined using the clientHeight property, as it represents the computed height of an element, including padding, but not margin. The following JavaScript function demonstrates this technique:

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;
}

This function effectively clones the properties of the target element into a temporary element, which is then used to calculate the line-height. By setting the font properties to "inherit" in the temporary element, we ensure that it adopts the same font family and size as the target element. This approach provides a reliable and consistent method for determining the actual rendered line-height, regardless of the presence of a CSS style rule.

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