Encode-Decode string count

decode-str.js

var fs = require('fs');
const readline = require('readline');

const getDecodedStr = async (filePath) => {
  let output = '';
  let charCounts = [];

  const rl = readline.createInterface({
    input: fs.createReadStream(filePath),
    crlfDelay: Infinity
  });

  for await (const line of rl) {
        let char = line;
        let parsedInt = parseInt(char);
        if (parsedInt == char) {
          charCounts.push(parsedInt);
        } else {
          let charRepeats = 0;
          let charRepeatCount = charCounts.length;
          let index = 0;
          while (charRepeatCount > 0) {
            charRepeats += charCounts[index] * 10 ** (charRepeatCount - 1);
            charRepeatCount--;
            index++;
          }
          while (charRepeats > 1) {
            output += char;
            charRepeats--;
          }
          output += char;
          charCounts = [];
        }
  }

  return output;
};

const main = async () => {
    const expectedOutput = 'AAAAAAAAAAAABBBCCCCCAAABCD';
    const encodeStr = await getDecodedStr('encoded-str.txt');

    console.log('expected output', expectedOutput);
    // console.log('actual output', encodeStr);
    console.log('test case passed', encodeStr === expectedOutput);
}

main()

decoded-str.txt

A
A
B
B
B
C
C
C
C
C
A
A
A
B
C

encode-str.js

var fs = require('fs');
const readline = require('readline');

const getEncodeStr = async (filePath) => {
    let prevChar = '';
  let output = '';
  let occurences = 0;

  const rl = readline.createInterface({
    input: fs.createReadStream(filePath),
    crlfDelay: Infinity
  });

  for await (const line of rl) {
        let char = line;
        if (char === prevChar) {
            occurences++;
          } else {
            output += `${occurences > 1 ?  occurences : ''}${prevChar}`;
            occurences = 1;
          }
          prevChar = char;
  }

  output += `${occurences > 1 ?  occurences : ''}${prevChar}`;

        return output;
};

const main = async () => {
    const expectedOutput = '2A3B5C3ABCD';
    const encodeStr = await getEncodeStr('decoded-str.txt');

    console.log('expected output', expectedOutput);
    console.log('actual output', encodeStr);
    console.log('test case passed', encodeStr === expectedOutput);
}

main()

encoded-str.txt

1
2
A
3
B
5
C
3
A
B
C
D