将字符串月、日、年转换为mm/dd/yyyy

function formatDate(dateString) {
  var parts = dateString.split('/'); // 假设输入的日期字符串格式为"月/日/年"
  var month = parts[0];
  var day = parts[1];
  var year = parts[2];

  // 处理月份
  if (month.length === 1) {
    month = '0' + month;
  }

  // 处理日期
  if (day.length === 1) {
    day = '0' + day;
  }

  // 处理年份
  if (year.length === 2) {
    var currentYear = new Date().getFullYear().toString().substr(-2);
    var currentCentury = new Date().getFullYear().toString().substr(0, 2);

    if (parseInt(year) < parseInt(currentYear)) {
      year = currentCentury + year;
    } else {
      year = (parseInt(currentCentury) - 1) + year;
    }
  }

  return month + '/' + day + '/' + year;
}

var inputDate = '6/1/21';
var formattedDate = formatDate(inputDate);
console.log(formattedDate); // 输出：06/01/2021