docs: function hasClass(element, className) {
    if (!assert(className && (typeof className === 'string'), 'Invalid class name: ' + className)) return false;
  
    let elements = [].concat(element);
    let n = elements.length;
  
    for (let i = 0; i < n; i++) {
      let e = elements[i];
      if (getClassIndex(e, className) < 0) return false;
    }
  
    return true;
  }