Can this condition be reduced?
if (!data.type || (data.type != 'coins' && data.type != 'shop' && data.type != 'free')) 
    return socket.emit('alert_message', {
        type: 'error',
        to: '',
        message: 'Invalid purchase type'
    });
Can this be simplified so that there are no duplicate data.type? data.type must be equal to free, coins or shop
