Adds one or more classes to document root for CSS tests. Classes persist through session.

style-tests.js

/**
 * Simple utility function to add special classes, prefixed with 'style-test' into
 * the document.
 *
 * Example:
 * ?style-test=test1+test2
 * Adds classes:  style-test-test1 style-test-test2
 *
 */
(function(Document, window) {
  function getParameterByName(name, url) {
    if (!url) url = window.location.href;
    name = name.replace(/[\[\]]/g, "\\$&");
    var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
      results = regex.exec(url);
    if (!results) return null;
    if (!results[2]) return '';
    return decodeURIComponent(results[2].replace(/\+/g, " "));
  }

  var root = document.documentElement, i, style_test, styles;
  if (sessionStorage) {
    style_test = sessionStorage.getItem('style-test');
  }
  if (getParameterByName('style-test')) {
    style_test = getParameterByName('style-test');
  }
  if (style_test) {
    styles = style_test.split(' ');
    for(i = 0; i < styles.length; i++) {
      root.classList.add('style-test-' + styles[i]);
    }
    if (sessionStorage) {
      sessionStorage.setItem('style-test', style_test);
    }
  }
})(Document, window);