Detect when ScrollBar reaches the bottom of the page

Javascript Course

The JavaScript function presented in this page can be used to Detect when ScrollBar reaches the bottom of the page.
This function is useful when you want to execute some JavaScript code when the user scrolls till the bottom of page, for example to display another content, making an infinite scroll.
Here is the function, named whenScrlBottom(). It must be accessed by the "onscroll" event.

// function to detect when scroollbar reaches the bottom of page
var whenScrlBottom = function() {
  // https://coursesweb.net/javascript/
  var win_h = (self.innerHeight) ? self.innerHeight : document.body.clientHeight;    // gets window height

  // gets current vertical scrollbar position
  var scrl_pos = window.pageYOffset ? window.pageYOffset : document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop;

  // if scrollbar reaces to bottom
  if (document.body.scrollHeight <= (scrl_pos + win_h)) {
    alert('Bottom');
  }
}

// register event on scrollbar
window.onscroll = whenScrlBottom;

<select name="a_name">
 <option value="val1">Option 1</option>
 <option value="val2" selected="selected">Option 2</option>
</select>

#id {
  background: linear-gradient(top left, #1f1, #fff, #11f);
}

var arr = [1, "CoursesWeb.net", "MarPlo.net"];
alert(arr[2]);

header("Location: http://coursesweb.net/");
exit;