code: function addClass(element, value) {
    if (!value) {
      return;
    }
  
    if (isNumber(element.length)) {
      forEach(element, function (elem) {
        addClass(elem, value);
      });
      return;
    }
  
    if (element.classList) {
      element.classList.add(value);
      return;
    }
  
    var className = element.className.trim();
  
    if (!className) {
      element.className = value;
    } else if (className.indexOf(value) < 0) {
      element.className = "".concat(className, " ").concat(value);
    }
  }
docs: Add classes to the given element.
  @param {Element} element - The target element.
  @param {string} value - The classes to be added.