rooms = {  

    '2B' : [    

        {"RoomEmailId":"2B-323@me.com","RoomName":"2B-323"},    

        {"RoomEmailId":"2B-123@me.com","RoomName":"2B-123"}     

    ],   

    '5A' : [  

        {"RoomEmailId":"5A-323@me.com","RoomName":"5A-323"},   

        {"RoomEmailId":"5A-123@me.com","RoomName":"5A-123"},  

        {"RoomEmailId":"5A-423@me.com","RoomName":"5A-423"}  

    ],  

    '1A' : [  

        {"RoomEmailId":"1A-323@me.com","RoomName":"1A-323"},  

        {"RoomEmailId":"1A-123@me.com","RoomName":"1A-123"},  

        {"RoomEmailId":"1A-423@me.com","RoomName":"1A-423"}  

    ]  

}

​

const result = Object.keys(rooms).reduce((obj, roomKey) => {

  obj[roomKey] = rooms[roomKey].slice().sort((a, b) => a.RoomName > b.RoomName);

  return obj;

}, {});

​

console.log(result); // the obj with each array value sorted

console.log(rooms); // note that the original object is unmodified