画像を遅延読み込みさせる DOMContentLoaded

<p><img data-src="test.svg" width="200px"></p>
<p><img data-src="test.svg" width="400px"></p>
<button>読込開始</button>

const myObj = new Map;

window.addEventListener("DOMContentLoaded", () => {
  const imgs = document.querySelectorAll("img");
  imgs.forEach((img) => {
    myObj.set(img, img.dataset.src);
    img.removeAttribute("src");
  });
});

const btn = document.querySelector("button");
btn.addEventListener("click", () => {
  const imgs = document.querySelectorAll("img");
  imgs.forEach((img) => {
      img.src = myObj.get(img);
  });
});