How Can I Get an HTML Element's Style Values in JavaScript Without Using External Libraries?

Obtaining HTML Element's Style Values in JavaScript

To retrieve style information from an HTML element that has been styled using the tag without using libraries, you can access the computed style rather than the inline style.

Cross-Browser Compatibility

IE uses the element.currentStyle property, while other browsers implement the DOM Level 2 document.defaultView.getComputedStyle(el, null).getPropertyValue(styleProp) method. To handle this difference, a cross-browser function is provided:

To obtain the width value in the provided code snippet, use the following:

var boxWidth = getStyle(document.getElementById("box"), "width");