思路
比较相邻两个的字符的码点，如果差值在1，就是连续的，然后拼接字符串放到数组中

        const test = '1212345689';
        const continuityKeyWord = [];
        function isContinuity(a, b) {
            return b.codePointAt() - a.codePointAt() == 1;
        }
        
        let keyword = test[0];
        for (let i in test) {
            if (i > 0 && isContinuity(test[i - 1], test[i])) {
                keyword += test[i];
            } else {
                if (keyword.length > 1) continuityKeyWord.push(keyword);
                keyword = test[i];
            }
        }
        if (keyword.length > 1) continuityKeyWord.push(keyword);
        
        console.log(continuityKeyWord, Math.max(...continuityKeyWord));