如何在JavaScript中禁用以前的日期

// 获取当前日期
var currentDate = new Date();

// 获取今天的日期
var currentDay = currentDate.getDate();
var currentMonth = currentDate.getMonth();
var currentYear = currentDate.getFullYear();

// 获取日期选择器元素
var datePicker = document.getElementById("datePicker");

// 监听日期选择事件
datePicker.addEventListener("change", function() {
  // 获取所选日期
  var selectedDate = new Date(datePicker.value);
  
  // 获取所选日期的天、月和年
  var selectedDay = selectedDate.getDate();
  var selectedMonth = selectedDate.getMonth();
  var selectedYear = selectedDate.getFullYear();
  
  // 比较所选日期和当前日期
  if (selectedYear < currentYear || 
      (selectedYear === currentYear && selectedMonth < currentMonth) || 
      (selectedYear === currentYear && selectedMonth === currentMonth && selectedDay < currentDay)) {
    // 禁用以前的日期
    datePicker.value = "";
    alert("请选择一个未来的日期！");
  }
});