RunBust,
#коллекции-не-массивы
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.addEventListener('DOMContentLoaded', function() {
[].forEach.call( document.querySelectorAll('.block'), function(block) {
var br = block.getBoundingClientRect();
alert(br.top + window.pageYOffset);
});
});
</script>
</head>
<body>
<div class="block">БЛОК 1</div>
<br>
<div class="block">БЛОК 2</div>
<br>
<br>
<div class="block">БЛОК 3</div>
<br>
</body>
</html>