TypeError：sendTypingFromUser不是函数

Question

我正在使用socket.io创建一个消息页面。在它的键入部分，我收到一条错误消息，指出“ TypeError：sendTypingFromUser不是函数”。我已经分配了全局变量“ sendTypingFromUser” 到在模块.exports对象外部创建的函数“ sendTypingToChat”。一旦连接了socket.io，就应该将该函数分配给变量。在socket.on（'USER_CONNECTED'）中，我已将该变量分配给该函数。然后，我在socket.on（“ TYPING”）下调用了“ sendTypingFromUser”。

这是我的代码：

const io = require('./index.js').io

const { VERIFY_USER, USER_CONNECTED, USER_DISCONNECTED, 
        LOGOUT, COMMUNITY_CHAT, MESSAGE_RECIEVED, MESSAGE_SENT,
        TYPING, PRIVATE_MESSAGE  } = require('../components/Events')

const { createUser, createMessage, createChat } = require('../components/Factories')

let connectedUsers = { }

let communityChat = createChat()

module.exports = function(socket){

    // console.log('\x1bc'); //clears console
    console.log("Socket Id:" + socket.id);

    var sendMessageToChatFromUser;

    var sendTypingFromUser;

    //Verify Username
    // socket.on(VERIFY_USER, (nickname, callback)=>{
    //  if(isUser(connectedUsers, nickname)){
    //      callback({ isUser:true, user:null })
    //  }else{
    //      callback({ isUser:false, user:createUser({name:nickname, socketID:socket.id})})
    //  }
    // })

    //User Connects with username
    socket.on(USER_CONNECTED, (user)=>{
        console.log(user);

        user.socketID = socket.id
        connectedUsers = addUser(connectedUsers, user)
        socket.user = user

        sendMessageToChatFromUser = sendMessageToChat(user.name)
        sendTypingFromUser = sendTypingToChat(user.name)

        io.emit(USER_CONNECTED, connectedUsers)
        console.log(connectedUsers);
    })

    //User disconnects
    socket.on('disconnect', ()=>{
        if("user" in socket){
            connectedUsers = removeUser(connectedUsers, socket.user.name)

            io.emit(USER_DISCONNECTED, connectedUsers)
            console.log("Disconnect", connectedUsers);
        }
    })


    //User logsout
    socket.on(LOGOUT, ()=>{
        connectedUsers = removeUser(connectedUsers, socket.user.name)
        io.emit(USER_DISCONNECTED, connectedUsers)
        console.log("Disconnect", connectedUsers);
    })

    //Get Community Chat
    socket.on(COMMUNITY_CHAT, (callback)=>{
        callback(communityChat)
    })

    socket.on(MESSAGE_SENT, ({chatId, message})=>{
        sendMessageToChatFromUser(chatId, message)
    })

    socket.on(TYPING, ({chatId, isTyping})=>{
        sendTypingFromUser(chatId, isTyping)
    })

    socket.on(PRIVATE_MESSAGE, ({receiver, sender}) => {
        if(receiver in connectedUsers) {
            const newChat = createChat({ name: `${receiver}&${sender}`, users: [receiver, sender] })
            const receiverSocket = connectedUsers[receiver].socketID
            socket.to(receiverSocket).emit(PRIVATE_MESSAGE, newChat)
            socket.emit(PRIVATE_MESSAGE, newChat)
        }
    })

}

/*
* Returns a function that will take a chat id and a boolean isTyping
* and then emit a broadcast to the chat id that the sender is typing
* @param sender {string} username of sender
* @return function(chatId, message)
*/
function sendTypingToChat(user){
    return (chatId, isTyping)=>{
        io.emit(`${TYPING}-${chatId}`, {user, isTyping})
    }
}

/*
* Returns a function that will take a chat id and message
* and then emit a broadcast to the chat id.
* @param sender {string} username of sender
* @return function(chatId, message)
*/
function sendMessageToChat(sender){
    return (chatId, message)=>{
        io.emit(`${MESSAGE_RECIEVED}-${chatId}`, createMessage({message, sender}))
    }
}

/*
* Adds user to list passed in.
* @param userList {Object} Object with key value pairs of users
* @param user {User} the user to added to the list.
* @return userList {Object} Object with key value pairs of Users
*/
function addUser(userList, user){
    let newList = Object.assign({}, userList)
    newList[user.name] = user
    return newList
}

/*
* Removes user from the list passed in.
* @param userList {Object} Object with key value pairs of Users
* @param username {string} name of user to be removed
* @return userList {Object} Object with key value pairs of Users
*/
function removeUser(userList, username){
    let newList = Object.assign({}, userList)
    delete newList[username]
    return newList
}

/*
* Checks if the user is in list passed in.
* @param userList {Object} Object with key value pairs of Users
* @param username {String}
* @return userList {Object} Object with key value pairs of Users
*/
function isUser(userList, username){
    return username in userList
}