wonder compress first draft

compress.js

function compress(param) {
  const charsCount = {};

  let lastCharProcessed = null;

  let result = [];

  param.split("").forEach((s, idx, arr) => {
    if (!charsCount[s]) {
      charsCount[s] = 1;
    } else {
      charsCount[s] += 1;
    }

    if (lastCharProcessed !== s) {
      result.push(lastCharProcessed);
      if (charsCount[lastCharProcessed] > 1) {
        result.push(charsCount[lastCharProcessed]);
      }
      charsCount[lastCharProcessed] = 0;
    }

    if (idx === arr.length - 1) {
      result.push(s);
      if (charsCount[s] > 1) result.push(charsCount[s]);
    }
    lastCharProcessed = s;
  });

  return result.join("");
}

console.log("aabbccc", compress("aabbccc"), compress("aabbccc") === "a2b2c3");
console.log("abcd", compress("abcd"), compress("abcd") == "abcd");
console.log("abbaac", compress("abbaac"), compress("abbaac") == "ab2a2c");
console.log("abbbbbbbbbbbb", compress("abbbbbbbbbbbb"), compress("abbbbbbbbbbbb") == "ab12");