intersection-observer/observer-callback-arguments.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>IntersectionObserver: callback arguments</title>
<link rel="help" href="https://w3c.github.io/IntersectionObserver/#notify-intersection-observers-algo">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="log"></div>
<script>
"use strict";

async_test(t => {
  const io = new IntersectionObserver(function(entries, observer) {
    t.step(() => {
      assert_equals(this, io);
      assert_equals(arguments.length, 2);
      assert_true(Array.isArray(entries));
      assert_equals(entries.length, 1);
      assert_true(entries[0] instanceof IntersectionObserverEntry);
      assert_equals(observer, io);

      io.disconnect();
      t.done();
    });
  });

  io.observe(document.body);
}, "Callback is invoked with |this| value of IntersectionObserver and two arguments");
</script>