third_party/web_platform_tests/intersection-observer/isIntersecting-change-events.html

<!DOCTYPE html>
<meta name="viewport" content="width=device-width,initial-scale=1">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<style>
pre, #log {
  position: absolute;
  top: 0;
  left: 200px;
}
#root {
  position: absolute;
  top: 0;
  left: 0;
  width: 150px;
  height: 200px;
  overflow: scroll;
}
#target1, #target2, #target3, #target4 {
  width: 100px;
  height: 100px;
}
#target1 {
  background-color: green;
}
#target2 {
  background-color: red;
}
#target3 {
  background-color: blue;
}
#target4 {
  background-color: yellow;
}
</style>

<div id="root">
  <div id="target1"></div>
  <div id="target2"></div>
  <div id="target3"></div>
</div>

<script>
var entries = [];
var observer;
var target1, target2, target3, target4;
var root;

runTestCycle(function() {
  root = document.getElementById('root');
  target1 = document.getElementById('target1');
  target2 = document.getElementById('target2');
  target3 = document.getElementById('target3');
  assert_true(!!root, "root element exists.");
  assert_true(!!target1, "target1 element exists.");
  assert_true(!!target2, "target2 element exists.");
  assert_true(!!target3, "target3 element exists.");
  observer = new IntersectionObserver(function(changes) {
    entries = entries.concat(changes);
    window.testRunner.DoNonMeasuredLayout();
  }, { root: root });
  observer.observe(target1);
  observer.observe(target2);
  observer.observe(target3);
  entries = entries.concat(observer.takeRecords());
  assert_equals(entries.length, 0, "No initial notifications.");
  runTestCycle(step0, "Rects in initial notifications should report initial positions.");
}, "isIntersecting changes should trigger notifications.");
window.testRunner.DoNonMeasuredLayout();
window.testRunner.DoNonMeasuredLayout();

function step0() {
  assert_equals(entries.length, 3, "Has 3 initial notifications.");
  checkRect(entries[0].boundingClientRect, [0, 100, 0, 100], "Check 1st entry rect");
  assert_equals(entries[0].target.id, 'target1', "Check 1st entry target id.");
  checkIsIntersecting(entries, 0, true);
  checkRect(entries[1].boundingClientRect, [0, 100, 100, 200], "Check 2nd entry rect");
  assert_equals(entries[1].target.id, 'target2', "Check 2nd entry target id.");
  checkIsIntersecting(entries, 1, true);
  checkRect(entries[2].boundingClientRect, [0, 100, 200, 300], "Check 3rd entry rect");
  assert_equals(entries[2].target.id, 'target3', "Check 3rd entry target id.");
  checkIsIntersecting(entries, 2, true);
  runTestCycle(step1, "Set scrollTop=100 and check for no new notifications.");
  target1.style.marginTop = "-100px";
  target2.style.marginTop = "-100px";
  target3.style.marginTop = "-100px";
  //root.scrollTop = 100;
  window.testRunner.DoNonMeasuredLayout();
}

function step1() {
  assert_equals(entries.length, 3, "Has 3 total notifications because isIntersecting did not change.");
  runTestCycle(step2, "Add 4th target.");
  target1.style.marginTop = "0px";
  target2.style.marginTop = "0px";
  target3.style.marginTop = "0px";
  //root.scrollTop = 0;
  target4 = document.createElement('div');
  target4.setAttribute('id', 'target4');
  root.appendChild(target4);
  observer.observe(target4);
}

function step2() {
  assert_equals(entries.length, 4, "Has 4 total notifications because 4th element was added.");
  checkRect(entries[3].boundingClientRect, [0, 100, 300, 400], "Check 4th entry rect");
  assert_equals(entries[3].target.id, 'target4', "Check 4th entry target id.");
  checkIsIntersecting(entries, 3, false);
  assert_equals(entries[3].intersectionRatio, 0, 'target4 initially has intersectionRatio of 0.');
  runTestCycle(step3, "Set scrollTop=100 and check for one new notification.");
  target1.style.marginTop = "-100px";
  target2.style.marginTop = "-100px";
  target3.style.marginTop = "-100px";
  target4.style.marginTop = "-100px";
  //root.scrollTop = 100;
}

function step3() {
  assert_equals(entries.length, 5, "Has 5 total notifications.");
  checkRect(entries[4].boundingClientRect, [0, 100, -100, 000], "Check 5th entry rect");
  assert_equals(entries[4].target.id, 'target4', "Check 5th entry target id.");
  checkIsIntersecting(entries, 4, true);
  assert_equals(entries[4].intersectionRatio, 0, 'target4 still has intersectionRatio of 0.');
  root.scrollTop = 0; // reset to make it easier to refresh and run the test
}

</script>