var nickNames = {};handleMessageBroadcasting = function(socket, nickNames){    socket.on('message', function(message){        socket.broadcast.to(message.room).emit('message', {            text: nickNames[socket.id] + ': ' + message.text        });    });};handleMessageBroadcasting(socket, nickNames);上面handleMessageBroadcasting函數內部用到了nickNames，我是將nickNames當參數傳入再使用呢？還是直接當成全局變量來使用好呢？為什么？