Matt Day’s in-place permutation algorithm using JavaScript generators

permute.js

function* allPermutationsOf(array, level=0) {
	array = array.slice(0);
	const calling = (level === array.length-1);
	let index = level;
	do {
		if (calling) yield array;
		else yield *allPermutationsOf(array, level+1);

		if (index > 0) {
			const tmp = array[index];
			array[index] = array[index-1];
			array[index-1] = tmp;
		}
	} while (index-- > 0);
}

for (const a of allPermutationsOf([1,2,3])) console.log(a);