function toggleClass(element, className) {
  if (!element || !className) {
    return
  }
  let classString = element.className
  const nameIndex = classString.indexOf(className)
  if (nameIndex === -1) {
    classString += '' + className
  } else {
    classString =
      classString.substr(0, nameIndex) +
      classString.substr(nameIndex + className.length)
  }
  element.className = classString
}
@param {HTMLElement} element
@param {string} className