const minifyString = (string) => {
  // your code here...
};
 
console.log(minifyString("aaaawwwweerrr")); // '3a4w2e3r'

const minifyString = (str) => {
  let res = "";
 
  const newObj = str.split("").reduce((acc, el) => {
    acc[el] = (acc[el] || 0) + 1;
    return acc;
  }, {});
 
  const newArr = Object.entries(newObj);
 
  for (let i = 0; i < newArr.length; i++) {
    res += newArr[i][1] + newArr[i][0];
  }
 
  return res;
};
 
console.log(minifyString("aaaawwwweerrr")); // '4a4w2e3r'