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Test Info:
- This WPT test may be referenced by the following Test IDs:
- /dom/window-print-mozPrintCallback-async-001.html - WPT Dashboard Interop Dashboard
<!doctype html>
<meta charset="utf-8">
<title>
Test for window.print(), with mozPrintCallback making async call to obj.done
</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<canvas id="myCanvas" width="80" height="80"></canvas>
<script>
let t = async_test(
"window.print(), with mozPrintCallback making async call to obj.done"
);
// mozPrintCallback needs to ensure that obj.done() will be called, as a signal
// that it's done with its rendering work. Here, we make that call via an async
// task, scheduled via setTimeout, to mimic the asynchronous work that's
// involved in real-life mozPrintCallback scenarios (e.g. PDF.js waiting for
// assets like fonts to be ready before it can render the content).
myCanvas.mozPrintCallback = function (obj) {
setTimeout(() => {
obj.done();
}, 0);
};
// window.print shouldn't block the main thread for any substantial time here.
//
// To validate this expectation, we see how soon after calling window.print()
// we're able to execute another task on the main thread (scheduled via
// requestAnimationFrame), and we expect the delay to be (substantially) less
// consistently overshooting this, because window.print would spawn a task that
// would block the main thread until the page print timer "watchdog" kicked in
// after ~10 seconds.)
const TOO_LONG_WINDOW_PRINT_DUR = 5000; // 5 seconds
window.addEventListener("load", () => {
let timestampBeforePrint = performance.now();
window.print();
// See how soon we're able to execute another task, scheduled via rAF:
requestAnimationFrame(
t.step_func(function () {
let timestampAfterPrint = performance.now();
let printDur = timestampAfterPrint - timestampBeforePrint;
assert_less_than(
printDur,
TOO_LONG_WINDOW_PRINT_DUR,
"window.print shouldn't block main thread for too long."
);
t.done();
})
);
});
</script>