strCount

function strLetterCount (str){
    // create an object to store each letter
    const countObj = {}
    // iterate over the string
    for (let i = 0; i < str.length; i++) {
        // if the letter isn't stored in the object, add it with a count of one
        if (!countObj[str[i]]) {
            countObj[str[i]] = 1;
        } else {
            // if the letter is already in the object, increment the count
            countObj[str[i]]++;
        }
    }
    // create a string to add the letter / count to
    let outStr = "";
    // iterate over the object to create the string
    for (const letter in countObj) {
        outStr += `${letter}${countObj[letter]}`;
    }
    // return the string
    return outStr;
}