Question

In jQuery, I can get a CSS property value for a selector using the css method and passing a property name, for example:

$('#myElement').css('backgroundImage');

My question is, how can I get a css property value from a class that is not yet applied to any element? Similar to $('.myClass').css('backgroundImage'); where the selector returns zero elements but there is a CSS declaration for that class.

Answer 1

You can create a temporary element without adding it to the DOM, and inspect the relevant property. CSS will apply, even if the element is not added to the DOM. E.g.

CSS

p { color: red; }

JS

var p = document.createElement('p');
alert(window.getComputedStyle(p, null).getPropertyValue('color'));

will give you the color value, but not add anything to the DOM.

WARNING

After a bit of research, I’ve determined that this method only works in Gecko-based browsers, so is not suitable for general-purpose use. This situation may change in future, but I wouldn’t rely on this if you want a cross-browser solution today.

Given that, I would suggest you just create a temporary element, add the desired class, add it to the document, inspect it to get the style value, then remove it. You can additionally apply styles such as display: none to prevent it from being shown to the user during the incredibly brief time that it’s part of the document.