gecko-dev/testing/web-platform/tests/intersection-observer/multiple-targets.html

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<!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;
}
.spacer {
height: calc(100vh + 100px);
}
.target {
width: 100px;
height: 100px;
margin: 10px;
background-color: green;
}
</style>
<div class="spacer"></div>
<div id="target1" class="target"></div>
<div id="target2" class="target"></div>
<div id="target3" class="target"></div>
<script>
var entries = [];
var target1, target2, target3;
runTestCycle(function() {
target1 = document.getElementById("target1");
assert_true(!!target1, "target1 exists.");
target2 = document.getElementById("target2");
assert_true(!!target2, "target2 exists.");
target3 = document.getElementById("target3");
assert_true(!!target3, "target3 exists.");
var observer = new IntersectionObserver(function(changes) {
entries = entries.concat(changes)
});
observer.observe(target1);
observer.observe(target2);
observer.observe(target3);
entries = entries.concat(observer.takeRecords());
assert_equals(entries.length, 0, "No initial notifications.");
runTestCycle(step0, "First rAF.");
}, "One observer with multiple targets.");
function step0() {
document.scrollingElement.scrollTop = 150;
runTestCycle(step1, "document.scrollingElement.scrollTop = 150");
assert_equals(entries.length, 3, "Three initial notifications.");
assert_equals(entries[0].target, target1, "entries[0].target === target1");
assert_equals(entries[1].target, target2, "entries[1].target === target2");
assert_equals(entries[2].target, target3, "entries[2].target === target3");
}
function step1() {
document.scrollingElement.scrollTop = 10000;
runTestCycle(step2, "document.scrollingElement.scrollTop = 10000");
assert_equals(entries.length, 4, "Four notifications.");
assert_equals(entries[3].target, target1, "entries[3].target === target1");
}
function step2() {
document.scrollingElement.scrollTop = 0;
runTestCycle(step3, "document.scrollingElement.scrollTop = 0");
assert_equals(entries.length, 6, "Six notifications.");
assert_equals(entries[4].target, target2, "entries[4].target === target2");
assert_equals(entries[5].target, target3, "entries[5].target === target3");
}
function step3() {
assert_equals(entries.length, 9, "Nine notifications.");
assert_equals(entries[6].target, target1, "entries[6].target === target1");
assert_equals(entries[7].target, target2, "entries[7].target === target2");
assert_equals(entries[8].target, target3, "entries[8].target === target3");
}
</script>