[js] 顶栏倒计时

效果是在顶栏添加一行文本：

JS 代码片段：

// 顶栏倒计时 JS片段
// author by JeffreyChen https://ld246.com/article/1728048965009
(function() {
  // 清除之前可能的定时器
  if (window.__countdownInterval) {
    clearInterval(window.__countdownInterval);
    window.__countdownInterval = null;
  }

  // 设置标题，替换样式
  const baseMessage = '距离<span style="color: red;"> 蓝桥杯 </span>剩余';
  const targetDate = new Date('2025-04-14');
  const toolbarSelector = '#toolbar > #drag';
  let countdownElement = null; // 倒计时元素缓存
  let lastDaysLeft = null; // 存储上一次的剩余天数
  let initializeAttempts = 0; // 初始化重试计数

  function calculateDaysLeft() {
    const currentDate = new Date();
    const differenceInTime = targetDate - currentDate;
    return Math.max(Math.ceil(differenceInTime / (1000 * 3600 * 24)) - 1, 0);
  }

  function updateCountdown() {
    const daysLeft = calculateDaysLeft();
    if (daysLeft !== lastDaysLeft) { // 仅在剩余天数更新时改变 DOM
      if (countdownElement) {
        countdownElement.innerHTML = `${baseMessage} ${daysLeft} 天`;
        lastDaysLeft = daysLeft; // 更新上一次的剩余天数
      }
    }
  }

  function insertCountdownElement() {
    if (!countdownElement) {
      const toolbarDrag = document.querySelector(toolbarSelector);
      if (toolbarDrag) {
        countdownElement = document.getElementById("countdown_days_display");
        if (!countdownElement) {
            toolbarDrag.insertAdjacentHTML(
              "afterend",
              `<div id="countdown_days_display" 
                    style="font-size: 12px; color: var(--b3-toolbar-color); margin-right: 14px; user-select:none;">
              </div>`
            );
            countdownElement = document.getElementById("countdown_days_display");
        }
        updateCountdown(); // 初次载入后立即更新倒计时
        initializeAttempts = 0; // 重置初始化重试计数
        // 设置新的定时器并保存ID到全局变量
        window.__countdownInterval = setInterval(updateCountdown, 60 * 1000); // 每60秒更新一次
      }
    }
  }
  
  function tryInitializeCountdown() {
    insertCountdownElement();
    if (!countdownElement && initializeAttempts < 5) {
      initializeAttempts++;
      console.error(`无法找到指定的工具栏挂载点或倒计时元素，第${initializeAttempts}次重试`);
      setTimeout(tryInitializeCountdown, Math.min(3000 * initializeAttempts, 15000)); // 指数退避重试延迟
    }
  }

  tryInitializeCountdown();
})();

鸣谢

[js] 全屏和刷新按钮、右上角倒计时