updateStyleRule.ts

/**
 * Update a style in the stylesheet.  This is very unfunctional, but unfortunately due to Javascript's ridiculous array-like
 * objects this is the only efficient way to do it.
 *
 * @param {Document} doc
 * @param {string} cssSelector
 * @param {(style: CSSStyleDeclaration) => void} updater
 * @returns {boolean}
 */
function updateStyleRule(doc: Document, cssSelector: string, updater: (style: CSSStyleDeclaration) => void): boolean {
  const stylesheets = doc.styleSheets || document.styleSheets;
  for (let n = 0; n < stylesheets.length; n++) {
    const stylesheet: CSSStyleSheet = <CSSStyleSheet>stylesheets.item(n);
    for (let i = 0; i < stylesheet.rules.length; i++) {
      const rule = stylesheet.rules.item(i);
      if (rule.type === rule.STYLE_RULE && (<CSSStyleRule>rule).selectorText === cssSelector) {
        updater((<CSSStyleRule>rule).style);
        return true;
      }
    }
  }

  return false;
}