compress.js

const compress = (str) => {
  if (str.length < 2) {
    return str;
  }

  const arr = str.split("");
  let oputput = [];
  let count = 1;

  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === arr[i + 1]) {
      count += 1;
    } else {
      const char = count === 1 ? `${arr[i]}` : `${arr[i]}x${count}`;
      oputput.push(char);
      count = 1;
    }
  }

  return oputput.join("");
};

console.log(compress("aaaaaabbbcaaa")); // ax4ca