https://only-to-top.github.io/Async-img
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<img data-src="https://picsum.photos/200" alt="">
<img data-src="https://picsum.photos/201" alt="">
<img data-src="https://picsum.photos/202" alt="">
<img data-src="https://picsum.photos/203" alt="">
<img data-src="https://picsum.photos/204" alt="">
<img data-src="https://picsum.photos/205" alt="">
<script>
(async ()=> {
for (let node of document.getElementsByTagName('img')) {
await new Promise(res=> {
node.src=node.dataset.src;
node.onload = ()=>res();
})
}
})();
//Используется data-src вместо src
</script>
</body>
</html>