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<!DOCTYPE html>
<meta charset="utf8">
<script>
window.onload = async () => {
parent.postMessage("ready", "*");
}
window.addEventListener("message", async function listener(event) {
if (event.data[0] == "gimme") {
var iframe = document.createElement("iframe");
iframe.src = "about:blank?foo";
document.body.append(iframe);
function test() {
let result = {
hardwareConcurrency : navigator.hardwareConcurrency
};
window.parent.document.querySelector("#result").textContent = JSON.stringify(result);
}
iframe.contentWindow.eval(`(${test})()`);
parent.postMessage(JSON.parse(document.querySelector("#result").textContent), "*")
}
});
</script>
<output id="result"></output>