Javascript 使用indexedDB时没有来自sendMessage的响应

我正在使用indexedDB编写一个chrome扩展，希望使用sendMessage将数据从后台页面传递到弹出窗口。
如果按下该按钮，将从弹出窗口向后台发送一条消息，并将响应写入“结果”div。 日志消息都正常，但在“openRequest.onsuccess”块中没有发送响应

我不确定为什么没有从openRequest.onsuccess接收到响应，但在写入控制台消息之后，控制台消息仍然没有收到

console.log的输出
弹出窗口
processMessage（）-2

背景
processMessage（）-2
processMessage（）-1

结果的内容
processMessage（）-2

popup.js

var popupInst;
var popupPage = function() {
    var mThis = this;
    this.msg;
    this.init = function() {
        document.querySelector('#btnAdd').addEventListener('click', this.add);
    };
    this.add = function() {
        chrome.extension.sendMessage({ add: { keyName: 'key', valueName: 'value' }}, function(response) {
            mThis.msg = (response.msg)
            console.log(mThis.msg);
            $('#results').empty().append(mThis.msg);
        });
    };
}
document.addEventListener('DOMContentLoaded', function(){popupInst = new popupPage(); popupInst.init();});

var bgInst;
var backgroundPage = function()
{
    var mThis = this;
    this.dbName = 'test-db';
    this.db;
    this.init = function() {
        var openRequest = window.indexedDB.open(mThis.dbName,1);
        openRequest.onsuccess = function(evt) {
            this.db = openRequest.result;
        };
        openRequest.onupgradeneeded = function(evt) {
            var objStore = evt.target.result.createObjectStore(this.dbName,{keyPath:"keyName"});
            objStore.createIndex("keyName","keyName",{unique:true});
            objStore.createIndex("valueName","valueName",{unique:false});
        };
        chrome.extension.onMessage.addListener(this.processMessage);
    };
    this.processMessage = function(msgRequest,msgSender,msgCallback) {
        if(msgRequest.add) {
            var openRequest = window.indexedDB.open(mThis.dbName);
            openRequest.onsuccess = function(evt) {
                var str1 = 'processMessage() - 1';
                msgCallback({ msg: str1 }); -> this message is never received in popup.js
                console.log(str1);          -> but this message is written to the log
            };
            var str2 = 'processMessage() - 2';
            msgCallback({ msg: str2 });
            console.log(str2);
        }
    };
}
document.addEventListener('DOMContentLoaded', function(){bgInst = new backgroundPage(); bgInst.init();});

background.js

var popupInst;
var popupPage = function() {
    var mThis = this;
    this.msg;
    this.init = function() {
        document.querySelector('#btnAdd').addEventListener('click', this.add);
    };
    this.add = function() {
        chrome.extension.sendMessage({ add: { keyName: 'key', valueName: 'value' }}, function(response) {
            mThis.msg = (response.msg)
            console.log(mThis.msg);
            $('#results').empty().append(mThis.msg);
        });
    };
}
document.addEventListener('DOMContentLoaded', function(){popupInst = new popupPage(); popupInst.init();});

var bgInst;
var backgroundPage = function()
{
    var mThis = this;
    this.dbName = 'test-db';
    this.db;
    this.init = function() {
        var openRequest = window.indexedDB.open(mThis.dbName,1);
        openRequest.onsuccess = function(evt) {
            this.db = openRequest.result;
        };
        openRequest.onupgradeneeded = function(evt) {
            var objStore = evt.target.result.createObjectStore(this.dbName,{keyPath:"keyName"});
            objStore.createIndex("keyName","keyName",{unique:true});
            objStore.createIndex("valueName","valueName",{unique:false});
        };
        chrome.extension.onMessage.addListener(this.processMessage);
    };
    this.processMessage = function(msgRequest,msgSender,msgCallback) {
        if(msgRequest.add) {
            var openRequest = window.indexedDB.open(mThis.dbName);
            openRequest.onsuccess = function(evt) {
                var str1 = 'processMessage() - 1';
                msgCallback({ msg: str1 }); -> this message is never received in popup.js
                console.log(str1);          -> but this message is written to the log
            };
            var str2 = 'processMessage() - 2';
            msgCallback({ msg: str2 });
            console.log(str2);
        }
    };
}
document.addEventListener('DOMContentLoaded', function(){bgInst = new backgroundPage(); bgInst.init();});

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看看这个答案：谢谢，现在可以了！可能重复的