Question

How do I set CSS properties of .anyclass:before or .anyclass:after via javascript?

Answer 1

Expanding on my comment:

:before and :after are not properties, they are CSS selectors. Therefore you cannot set them on some element, you can only add rules with such selectors to a stylesheet.

If you want to add DOM nodes before or after all elements that match a given selector with jQuery, you can use the before and after methods respectively.

If you want to add CSS rules to the current page, you can use the DOM level 2 CSSStyleSheet interface. A minimal example would look like this:

// Note: this is sample code. Do not use it blindly in your own page.
document.styleSheets[0].insertRule(".foo:before { /* something */ }", 0);

See the MDN documentation for insertRule for more example code.