socks.js

socks.js

function wash(socks) {
	var socksYouHave = [];
	var sockSizes = ['small', 'medium', 'large'];
	socks.forEach(function(sock) {
		// Weird socks never survive
		if(sockSizes.indexOf(sock) === -1) return;
		
		// One in ten socks never make it out alive
		if(Math.floor(Math.random() * 10) === 0) return;
		
		// Some socks just change
		if(Math.floor(Math.random() * 10) < 4) {
			socksYouHave.push(sockSizes[Math.floor(Math.random() * sockSizes.length)]);
			return;
		}
		socksYouHave.push(sock);
	});
    return socksYouHave;
}

console.log(wash([
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
	'medium',
]));

After 20-30 times (usually) you will have to buy new socks D: