How Can I Reliably Retrieve and Update Font Size in HTML, Even When Defined in a Stylesheet?

Retrieving Font Size in HTML

In HTML, the font size of an element can be specified using CSS. Typically, the style.fontSize property is used to set or retrieve the font size. However, retrieving the font size can be challenging if it is defined in a stylesheet.

Using style.fontSize

The following example attempts to retrieve and then update the font size of an element using style.fontSize:

var x = document.getElementById("foo").style.fontSize;
document.getElementById("foo").style.fontSize = x + 1;

This code, however, may not work if the font-size is defined externally in a CSS stylesheet. In such cases, style.fontSize will return an empty string, which can lead to unexpected results.

Using window.getComputedStyle

To accurately retrieve the font size, even when it is defined in a stylesheet, use the window.getComputedStyle method. This method calculates the actual style of the element:

var el = document.getElementById('foo');
var style = window.getComputedStyle(el, null).getPropertyValue('font-size');
var fontSize = parseFloat(style); // Converts the retrieved value to a float
el.style.fontSize = (fontSize + 1) + 'px'; // Updates the font size

By utilizing window.getComputedStyle, you can reliably retrieve and update the font size of an element, regardless of how it is defined in the stylesheet.

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