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onmessage = function (e) {
const message = e.data;
if (message === "IsETPAllowListed") {
sendMessage(!isOffscreenAPlaceHolder());
}
};
function isOffscreenAPlaceHolder() {
const canvas = new OffscreenCanvas(4, 4);
const context = canvas.getContext("2d");
// An empty canvas would return 0,0,0,0 for the pixel data.
return !context.getImageData(0, 0, 4, 4).data.every(el => el === 0);
}
function sendMessage(message) {
self.clients.matchAll({ includeUncontrolled: true }).then(function (res) {
if (!res.length) {
dump("Error: no clients are available.\n");
return;
}
res[0].postMessage(message);
});
}