get all interna, external and data URLs present inside a stylesheet

getURLsFromCSS.js

/**
 * @description Returns all image/font/whatever URLs from all stylesheets present in the document
 * @param styles {object|StyleSheetList} https://developer.mozilla.org/en-US/docs/Web/API/StyleSheetList
 * @returns {array|string}
 */
function getURLsFromCSS(styles) {
    var urls = [];
    
    for (var x in styles) {
        var style = styles[x];
        var rules = style.rules;
        for (var y in rules) {
            var rule = rules[y];
            var text = rule.cssText;
            var match = text && text.match(/url\((.*?)\)/)
            if (!!match) {
                var url = match[1].replace(/('|")/g, '');
                urls.push(url);
            }
        }
    }
    return urls;
}

//demo
var styles = window.document.styleSheets;
getURLsFromCSS(styles); // ["/images/spinners/octocat-spinner-64.gif","/images/modules/jobs/logo.png","http://example.com/images/modules/pulls/progressive-disclosure-line@2x.png", "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAnsC7BpEAAAAABJRU5ErkJggg=="]