mix

function mix(a, b)
{
    const alphabet = "abcdefghijklmnopqrstuvwxyz".split('');
    let prepare = function (str) {
        let freq = {};
        str.split('').forEach(function (letter) {
            if (letter != letter.toUpperCase()) {
                freq[letter] = typeof freq[letter] == "undefined" ? 1 : freq[letter] + 1;
            }
        });
        return freq;
    };
    const left = prepare(a);
    const right = prepare(b);
    let result = [];
    alphabet.forEach(function (letter) {
        if (left[letter] > 1 || right[letter] > 1) {
            const code = left[letter] == right[letter] ? '='
                : left[letter] > right[letter] ? '1' : '2';
            result.push(code + ':' + letter.repeat(Math.max(left[letter], right[letter])));
        }
    });
    result.sort((a, b) => b.length - a.length);
    return result.join('/');
}