login 함수 프로토콜 규격 맞추고 useCallback으로 변경

-import React, { useContext, useState } from 'react';
+import React, { useCallback, useContext, useState } from 'react';
 import { useHistory } from 'react-router';
 import { Main } from '../components/common/Main';
 import { MessageResponse, MessageType } from '../components/common/types';
@@ -9,15 +9,17 @@ export const Login: React.FC = () => {
     const socket = useContext(SocketContext);
     const [ username, setUsername ] = useState("");
 
-    const login = () => {
-      socket.emit(MessageType.LOGIN, username, (response : MessageResponse<null>) => {
+    const login = useCallback(() => {
+      console.log("emitted.");
+      socket.emit('msg', {type: MessageType.LOGIN, message: {username}}, (response : MessageResponse<undefined>) => {
+        console.log("responsed.");
         if (response.ok) {
           history.push('/rooms');
         } else {
           console.error('login error!'); // TODO: 팝업 에러?
         }
       });
-    }
+    }, []);
 
     return (
       <Main>