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That's great if it solves your problem, but I noticed that yours just makes a huge integer private key out of the dice rolls and not a base58 WIF
You should never do crypto in your browser. This includes using javascript for that.
It just hit me that there is a way to extract private keys from the browser even if you are offline.
Scripts have a local storage in the browser that stores keys and values, and if some site is foolhardy enough to save private keys or other secrets there, all someone has to do is exploit a browser CVE that let's you see any site's local storage and then steal the private key at a later date.