How Can I Reliably Get and Change Font Sizes in HTML?

Obtaining Font Size Values in HTML

The need to access and manipulate the font size of HTML elements arises frequently in web development. To do so effectively, it's crucial to understand the underlying mechanisms and potential pitfalls.

Attempting to retrieve the font size directly from the style.fontSize property may not always provide the desired result. In cases where the font size is defined in a stylesheet, the property value will be an empty string. To circumvent this issue, the window.getComputedStyle method is recommended. The code below demonstrates how to properly obtain and adjust the font size:

var el = document.getElementById('foo');
var style = window.getComputedStyle(el, null).getPropertyValue('font-size');
var fontSize = parseFloat(style); // Convert the value to a float for precision
el.style.fontSize = (fontSize + 1) + 'px'; // Apply the updated font size

This approach ensures that the font size is accurately retrieved, even if it's inherited from a stylesheet. The parseFloat function is used to convert the string value to a float, allowing for finer-grained adjustments in font size. By utilizing this technique, you can easily modify the font size of HTML elements and maintain consistency with stylesheet definitions.

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