JS，如何将不带分隔符的字符串格式化为日期

function formatDate(dateString) {
  var year = dateString.substring(0, 4);
  var month = dateString.substring(4, 6);
  var day = dateString.substring(6, 8);

  var yearInt = parseInt(year);
  var monthInt = parseInt(month) - 1;
  var dayInt = parseInt(day);

  var formattedDate = new Date(yearInt, monthInt, dayInt);

  return formattedDate;
}

var dateString = "20220101";
var formattedDate = formatDate(dateString);

console.log(formattedDate.getFullYear()); // 输出：2022
console.log(formattedDate.getMonth() + 1); // 输出：1
console.log(formattedDate.getDate()); // 输出：1