Get a clean ASCII string from a JavaScript string

cleanString.js

function cleanString(str, method, r) {
    var result = '',
        max = str.length,
        i, ch;

    for (i = 0; i < max; i++) {
        ch = str.charCodeAt(i);

        if (ch < 128) {
            result += str.charAt(i);
        } else {
            switch (method) {
                case 'elide':
                break;

                case 'replace':
                    result += r || '?'; 
                break;

                case 'entity':
                    result += '&#' + ch + ';';
                break;

                default: 
                    throw new Error();
            }
        }
    }

    return result;
}