Write a way to play mastermind.

Mastermind-solver.js

// The other player starts with a code that you are trying to guess
// the code is 4 digits 1-6, on each guess the other player will
// tell you the number of digits in your guess that are in the final solution
// and the exact number of digits that matches.
// e.g. code: '1234', guess: '1111' => '1 1'

const parse = (code) => code.split('').map((n) => parseInt(n, 10));

const MASTER_CODE = parse('1234');

const guess = (code) => code.filter((d, i) => d === MASTER_CODE[i]).length;

const setDigit = (code, position, digit) => {
  const digits = [...code];
  digits[position] = digit;
  return digits;
};

const solve = () => {
  let code = parse('1111');
  let prevMatches = guess(code);

  for (let position = 0; position < code.length; position++) {
    for (let digit = 2; digit <= 6; digit++) {
      const next = setDigit(code, position, digit);
      const matches = guess(next);
      if (matches < prevMatches) {
        continue;
      }

      if (matches > prevMatches) {
        code = next;
        prevMatches = matches;
      }
    }
  }

  return code.join('');
};

console.log(solve());