This implementation breaks Tesseract.js for users who do not have a browser that supports OffscreenCanvas, which includes all non-Chromium users who have not updated their browser recently. I'm not opposed to adding handling for OffscreenCanvas inputs, but that aspect needs to be fixed.

You're quite right of course.

The check I was using -- if(OffscreenCanvas) -- was inadequate and it still produced a ReferenceError in older browsers. I've replaced this with if (typeof OffscreenCanvas !== 'undefined'). To verify this, I downgraded to an older version of Firefox, v72.0.2 from January 2020, which does not natively support OffscreenCanvas. Before this change, I saw an error when running the Tesseract.js demo app -- after the commit, it works smoothly.

Thanks for your time and let me know if you notice any other problems.

Thanks for editing, as well as checking using the old version of the browser. The new implementation looks good, I will merge.