Playing Card Drawer

Builds a fresh 52-card deck (jokers optional), shuffles it, and deals off the top. Drawn cards stay drawn and the counter goes down, so you can keep dealing to the bottom without ever seeing a repeat — which is what separates a deck from a random-card generator, and what makes it usable for a card game, a probability lesson or any draw where the odds have to change as cards leave.

The shuffle is Fisher-Yates walked from the end of the array downward, swapping each position with a random index at or below it. That detail is the whole algorithm: the version that picks from the entire array on every step looks identical, runs just as fast, and produces a measurably skewed distribution — a classic bug that survived in production code for years because a biased shuffle still looks shuffled.

Randomness comes from crypto.getRandomValues rather than Math.random, and the reason is arithmetic. A deck has 52! orderings, which is roughly 8 × 10^67, a 68-digit number. A generator seeded with 128 bits of state can reach at most 2^128 of them — about 3 × 10^38 — so more than 99.999…% of possible decks are unreachable no matter how long you shuffle. Drawing fresh entropy from the operating system for each swap removes that ceiling. The one residual imperfection is modulo bias from folding a 32-bit value into a 52-way choice, which favours some positions by about one part in 80 million: real, and smaller than any effect you could detect in a lifetime of dealing.

What this cannot do is make a shuffle fair for a game where someone can see the screen. The deck lives in the tab, so anyone with the page open has the whole order in memory; this is a convenience for play among people who trust each other, not a card room. And a reshuffle really is a new deck — the discards do not come back in the order they left, so it is not a substitute for a cut.