<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<button data-val="test1" data-index="1">1</button>
<button data-val="test2" data-index="2">2</button>
<button data-val="test3" data-index="3">3</button>
<script>
let btns = document.querySelectorAll('button');
for(let i = 0; i < btns.length; i++){
btns[i].onclick = function(){
console.log(this.dataset)
}
}
</script>
</body>
</html>