If you want to get the pixels of the document scrolled to from the upper left corner of the window, then use the pageXoffset and pageYoffset property. Use pageYoffset for vertical pixels.
Example
You can try to run the following code to learn how to work with pageYOffset property in JavaScript.
<!DOCTYPE html>
<html>
<head>
<style>
div {
background-color: green;
height: 1500px;
width: 1500px;
}
</style>
</head>
<body>
<script>
function scrollFunc() {
window.scrollBy(200, 200);
alert("Vertical: " + window.pageYOffset);
}
</script>
<button onclick="scrollFunc()" style="position:fixed;">Scroll</button>
<br><br><br>
<div>
</div>
</body>
</html>