Codecademy: "Guess a Letter, Any Letter!"

//sample solution to Hangman Exercise 4

// Skip to guessLetter(). You shouldn't need to touch this function.
function alterAt ( n, c, originalString ) {
    return originalString.substr(0,n) + c + originalString.substr(n+1,originalString.length);
}

function guessLetter( letter, shown, answer ) {
    var checkLetter = -1;  // This variable will hold the indexOf()

    checkLetter = answer.indexOf(letter); // Single Argument Version starting at 0
    while ( checkLetter >= 0 ) {
       
        // Replace the letter in shown with alterAt() and then store in shown.
        shown = alterAt(checkLetter, letter, shown);
        // Use indexOf() again and store in checkLetter
        checkLetter = answer.indexOf(letter, checkLetter+1);
    }
   
    // Return our string, modified or not
    return shown;
}

//for testing purposes
console.log(guessLetter('a','______','banana'));
console.log(guessLetter('a','______','apples'));
console.log(guessLetter('a','______','futura'));