test_performance_now.html

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<!DOCTYPE HTML>

<html>

<head>

  <title>Test for High Resolution Timer</title>

  <script src="/tests/SimpleTest/SimpleTest.js"></script>

  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />

</head>

<body>

  <script>

    ok(window.performance, "Performance object should exist.");

    ok(typeof window.performance.now == 'function', "Performance object should have a 'now' method.");

    var n = window.performance.now(), d = Date.now();

    ok(n >= 0, "The value of now() should be equal to or greater than 0.");

    ok(window.performance.now() >= n, "The value of now() should monotonically increase.");

    SimpleTest.waitForExplicitFinish();

    SimpleTest.requestFlakyTimeout("using setTimeout() to measure performance.now()");

    // Spin on setTimeout() until performance.now() increases. Due to recent

    // security developments, the hr-time working group has not yet reached

    // consensus on what the recommend minimum clock resolution should be:

    // https://w3c.github.io/hr-time/#clock-resolution

    // Since setTimeout might return too early/late, our goal is for

    // performance.now() to increase before a 2 ms deadline rather than specific

    // number of setTimeout(N) invocations.

    // See bug 749894 (intermittent failures of this test)

    var checks = 0;

    function checkAfterTimeout() {

      checks++;

      var d2 = Date.now();

      var n2 = window.performance.now();

      // Spin on setTimeout() until performance.now() increases. Abort the

      // test if it runs for more than 2 ms or 50 timeouts.

      let elapsedTime = d2 - d;

      let elapsedPerf = n2 - n;

      if (elapsedPerf == 0 && elapsedTime < 2 && checks < 50) {

        setTimeout(checkAfterTimeout, 1);

        return;

      // Our implementation provides 1 ms resolution (bug 1451790).

      ok(elapsedPerf >= 1,

         `Loose - the value of now() should increase by no less than 1 ms ` +

         `after 2 ms. delta now(): ${elapsedPerf} ms`);

      // If we need more than 1 iteration, then either performance.now()

      // resolution is shorter than 1 ms or setTimeout() is returning too early.

      ok(checks == 1,

         `Strict - the value of now() should increase after one setTimeout. ` +

         `iters: ${checks}, dt: ${elapsedTime}, now(): ${n2}`);

      SimpleTest.finish();

};

    setTimeout(checkAfterTimeout, 1);

  </script>

</body>

</html>