Javascript淡入淡出彩色图像和背景

<div id="image" style="opacity: 0;">
  <img src="image.jpg" alt="彩色图像">
</div>

<div id="background" style="opacity: 0;">
  <p>彩色背景</p>
</div>

function fadeIn(element) {
  let opacity = 0;
  let timer = setInterval(function() {
    if (opacity >= 1) {
      clearInterval(timer);
    }
    element.style.opacity = opacity;
    opacity += 0.1;
  }, 100);
}

function fadeOut(element) {
  let opacity = 1;
  let timer = setInterval(function() {
    if (opacity <= 0) {
      clearInterval(timer);
    }
    element.style.opacity = opacity;
    opacity -= 0.1;
  }, 100);
}

let image = document.getElementById("image");
let background = document.getElementById("background");

fadeIn(image);
fadeOut(background);