JavaScript: Is element in viewport?

isElementInViewport.js

/*
No jQuery necessary.
Thanks to Dan's StackOverflow answer for this:
http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
*/

function isElementInViewport(el) {
  var rect = el.getBoundingClientRect();
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || document. documentElement.clientHeight) &&
    rect.right <= (window.innerWidth || document. documentElement.clientWidth)
  );
}

Hello Mistovic,
The (el) parameter is the DOM element that has been passed to the function to check if it is in the viewport or not yet.
Hello, and thank you for a reply.

So basically, we created a new element (el) with boundingClientRect() and gave him coordinates (or size) with return (top, left, bottom, right).
is that understood well?