Counting characters in a string for javascript

charCount.js

function charCount(str) {
    if (!str || typeof str !== 'string') {
        throw 'must provide a string';
    }
    var letter,
        countObj = {},
        alphabeticalLetters = [],
        outputString = '',
        letterCount;

    for (var i=0; i < str.length; ++i) {
        letter = str[i];
        if (letter in countObj) {
            countObj[letter] += 1;
        } else {
            countObj[letter] = 1;
            alphabeticalLetters.push(letter);
        }
    }
    alphabeticalLetters.sort();

    for (i = 0; i < alphabeticalLetters.length; ++i) {
        letter = alphabeticalLetters[i];
        letterCount = countObj[letter];
        if (letter === ' ') {
            outputString += "'" + letter + "'" + ':' + letterCount + ' ';
        } else {
            outputString += letter + ':' + letterCount + ' ';
        }
    }

    return outputString;
}

To use with google spreadsheets go to Drive homepage, click Create -> More -> Script and paste the above contents. Then in a spreadsheet use by doing =charCount(A1) in a cell.