<script>

if (window.testRunner)
    testRunner.waitUntilDone();

function load()
{
    setTimeout(() => {
        progress.value = 70;

        if (window.testRunner)
            testRunner.notifyDone();
    }, 0);
}

</script>
<body onload="load()">
<progress id="progress" max="100" value="50"></progress>