Cabinet of Curiosities

const s = "const s = %s;\nconsole.log(s.replace(\"%s\", JSON.stringify(s)));";
console.log(s.replace("%s", JSON.stringify(s)));

A Program That Writes Itself

JavaScript · 1960

// Primality testing with a regular expression.
//
// The number n becomes a string of n ones. The pattern then asks whether
// that string can be cut into two-or-more equal groups of two-or-more —
// which is exactly the question of whether n has a non-trivial factor.
const composite = /^1?$|^(11+?)\1+$/;

const isPrime = (n) => !composite.test("1".repeat(n));

const primes = [];
for (let n = 2; primes.length < 12; n++) {
	if (isPrime(n)) primes.push(n);
}

console.log(primes.join(" "));

Primes, By Regular Expression

JavaScript · 1998

// The Y combinator: recursion for a language that has none.
//
// Nothing below names itself. `fact` never says "fact", and yet it recurs.
const Y = (f) => ((x) => x(x))((x) => f((...args) => x(x)(...args)));

const fact = Y((recur) => (n) => (n <= 1 ? 1 : n * recur(n - 1)));

console.log([1, 2, 3, 4, 5, 6].map(fact).join(" "));

Recursion Without a Name

JavaScript · 1969

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Cabinet of Curiosities

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Cabinet of Curiosities

Shown as a list, because your system asks for reduced motion.