test_setInterval_from_start.html

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https://bugzilla.mozilla.org/show_bug.cgi?id=1252268

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  <title>Test for Bug 1378394</title>

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<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1378394">Mozilla Bug 1378394</a>

<script>

SimpleTest.waitForExplicitFinish();

// Some of our platforms are quite slow.  Use very large time values to

// try to avoid raciness.

const burnTimeMS = 5000;

const intervalTimeMS = 10000;

// The overall interval should include our callback "burn time".  So we

// expect the delay to be the remaining time.

const expectedDelayMS = intervalTimeMS - burnTimeMS;

// Allow some margin for error because of slow test platforms.

const allowedMarginMS = burnTimeMS / 2;

let id;

let lastEndTime;

function interval()

  let start = performance.now();

  if (lastEndTime !== undefined) {

    let delta = start - lastEndTime;

    ok(delta <= expectedDelayMS + allowedMarginMS,

       'interval should not fire too late');

    ok(delta >= expectedDelayMS - allowedMarginMS,

       'interval should not fire too early');

    clearInterval(id);

    SimpleTest.finish();

    return;

  while((performance.now() - start) < burnTimeMS);

  lastEndTime = performance.now();

id = setInterval(interval, intervalTimeMS);

</script>

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