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var sep = function(str) {
    var parts = (str + '').split('.'),
        main = parts[0],
        len = main.length,
        output = '',
        i = len - 1;

    while(i >= 0) {
        output = main.charAt(i) + output;
        if ((len - i) % 3 === 0 && i > 0) {
            output = ',' + output;
        }
        --i;
    }

    if (parts.length > 1) {
        output += '.' + parts[1];
    }
    return output;
};