count character occurrence in a word

strLetterCount.js

function strLetterCount(word) {
    /** 
     * initialize new key value pair (Map) where;
     *  key = character
     *  value = count
    */
    let characterCounts = new Map();

    /** 
     * loop through each character in the word
    */
    for (let i = 0; i < word.length; i++) {
        /** 
         * get the value (count) that is currently stored in our Map for the key (character)
         *  if we can't find the value, we will default the value (count) to 0
        */
        let characterCount = characterCounts.get(word[i]) ?? 0;

        /**
         * take the current value (count) we retrieved from our map 
         * for the key (character) we are currently iterating over
         * and add 1 to the count so it includes the current iteration
         */
        characterCounts.set(word[i], characterCount + 1);
    }

    /**
     * now we have completed the creation of our key value pair (Map)
     * that will have a key for each character in the input word and 
     * an associated value or count equal to the number of occurrences
     * for that character
     * 
        woof = 
            { key: w, value: 1 },
            { key: o, value: 2 },
            { key: f, value: 1 }
     * 
     */

    /**
     * initialize an empty string that will be our output from this method
     */
    let outputString = '';

    /**
     * for each [character, count] pair in our character counts map we
     * should append the character and count to our output stream
     */
    for (const [character, count] of characterCounts.entries()) {
        outputString += character + count;
    }

    /** 
     * finally we will return our output string
     */
    return outputString;
};