如何使用javascript在几秒钟后增加和减少不透明度？

// 增加不透明度
function increaseOpacity(element, targetOpacity, duration) {
  var currentOpacity = 0;
  var increment = targetOpacity / (duration * 1000 / 100); // 每100毫秒增加的透明度值

  var timer = setInterval(function() {
    currentOpacity += increment;
    element.style.opacity = currentOpacity;

    if (currentOpacity >= targetOpacity) {
      clearInterval(timer);
    }
  }, 100);
}

// 减少不透明度
function decreaseOpacity(element, targetOpacity, duration) {
  var currentOpacity = 1;
  var decrement = targetOpacity / (duration * 1000 / 100); // 每100毫秒减少的透明度值

  var timer = setInterval(function() {
    currentOpacity -= decrement;
    element.style.opacity = currentOpacity;

    if (currentOpacity <= targetOpacity) {
      clearInterval(timer);
    }
  }, 100);
}

// 使用示例
var element = document.getElementById('myElement'); // 替换为需要操作的元素的ID
increaseOpacity(element, 0.5, 2); // 在2秒钟后增加到0.5的不透明度
decreaseOpacity(element, 0, 3); // 在3秒钟后减少到完全透明