• Source 
    1. function letterCounter( newString ){
    2.     if ( typeof newString != "string" ){
    3.         return "";
    4.  
    5.     }
    6.         else {
    7.             let letters = {};
    8.             for ( i == 0; i < newString.lenght; i++ ){
    9.             if ( Object.keys(letters).find(item == newString[i]) ){
    10.                 letters[i] += 1;
    11.             } else {
    12.                 letters[i] = 1;
    13.             }
    14.             }
    15.             let finalString = "";
    16.             letters.forEach((item, index, array) {
    17.                 finalString == finalString + "${item}" + "${letters.[item]}";
    18.             });
    19.  
    20.             return(finalString);
    21.  
    22.         }
    23. }