How to Calculate Actual Line-Height in JavaScript?

Determining Actual Line-Height with JavaScript

In web development, it's essential to understand the actual line-height of an element, especially when working with text content. While the style.lineHeight property provides the CSS-defined line-height, sometimes the actual line-height may differ due to the absence of specific CSS rules.

Calculating Actual Line-Height

To calculate the actual line-height of an element using JavaScript, we can utilize the .clientHeight property. This approach is not entirely reliable, but it offers a practical method to determine the line-height in the absence of CSS definitions.

Code Implementation

The following code snippet demonstrates how to calculate the actual line-height using .clientHeight:

function getLineHeight(el) {
    var temp = document.createElement(el.nodeName), ret;
    temp.setAttribute("style", "margin:0; padding:0; "
        + "font-family:" + (el.style.fontFamily || "inherit") + "; "
        + "font-size:" + (el.style.fontSize || "inherit"));
    temp.innerHTML = "A";

    el.parentNode.appendChild(temp);
    ret = temp.clientHeight;
    temp.parentNode.removeChild(temp);

    return ret;
}

Explanation

The function operates by cloning the properties of the target element into a temporary element. By rendering a single character ("A") within the temporary element, it effectively mimics the line-height behavior of the original element. The clientHeight of this temporary element is then captured as the actual line-height. Finally, the temporary element is removed from the DOM.

Conclusion

This method provides a reliable way to determine the actual line-height of an element in JavaScript, regardless of any existing CSS definitions. It's especially useful for dynamic content where CSS control may not be feasible.

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