LayoutTests/performance-api/performance-observer-nested.html

<!DOCTYPE HTML>
<html>
<head>
<script src="../resources/js-test-pre.js"></script>
</head>
<body>
<script>
description("Test PerformanceObserver handling of entries added while in callback.");
window.jsTestIsAsync = true;

window.callbackCount = 0;
window.list = null;

let observer1 = new PerformanceObserver((list) => {
    window.list = list;
    callbackCount++;
    testPassed("PerformanceObserver 1 callback fired");

    if (callbackCount === 1) {
        performance.mark("mark2");
        shouldBe(`list.getEntries().length`, `1`);
    } else if (callbackCount === 3) {
        shouldBe(`list.getEntries().length`, `2`);
    } else {
        testFailed("Unexpected callback count");
        finishJSTest();
    }

    for (let mark of list.getEntries())
        debug(" - " + mark.name);
});

let observer2 = new PerformanceObserver((list) => {
    window.list = list;
    callbackCount++;
    testPassed("PerformanceObserver 2 callback fired");

    if (callbackCount === 2) {
        performance.mark("mark3");
        shouldBe(`list.getEntries().length`, `2`);
    } else if (callbackCount === 4) {
        shouldBe(`list.getEntries().length`, `1`);
    } else {
        testFailed("Unexpected callback count");
        finishJSTest();
    }

    for (let mark of list.getEntries())
        debug(" - " + mark.name);

    if (callbackCount === 4)
        finishJSTest();
});

observer1.observe({entryTypes: ["mark"]});
observer2.observe({entryTypes: ["mark"]});
performance.mark("mark1");
</script>
<script src="../resources/js-test-post.js"></script>
</body>
</html>