code: function metriclcs(s1, s2) {
    if (typeof s1 !== "string" || typeof s1 !== "string") return NaN;
    if (s1 === s2) return 1;
  
    const mlen = Math.max(s1.length, s2.length);
    if (mlen === 0) return 1;
    return lcsLength(s1, s2) / mlen;
  }
docs: Returns a number between 1 and 0, where 1 means they are exactly the same and 0 means no common subsequences.
  If either string is not a string, returns NaN
  @param {string} s1
  @param {string} s2
  @returns {number}