recently, I intend to cache chat data locally. I encountered some problems in the process of using indexedDB,. The code is as follows

let db;
let chatDB = {
    indexedDB: window.indexedDB || window.webkitIndexedDB || window.mozIndexedDB || window.msIndexedDB,
    // 
    openDB: function (dbname, version, store) {
        let request = this.indexedDB.open(dbname, version || 1)
        //
        request.onupgradeneeded = function (event) {
            //
            db = event.target.result;
            //........
        };
        //
        request.onerror = function (e) {
            console.log(e.currentTarget.error.message);
        };
        //
        request.onsuccess = function (e) {
            db = e.target.result;
        };
    },
    //
    addData: function (storeName, data) {
        let store = db.transaction(storeName, "readwrite").objectStore(storeName)
        let request = store.add(data);
        request.onerror = function () {
            console.error("add")
        };
        request.onsuccess = function () {
            console.log("add")
        };
    }
}
chatDB.openDB(name,version);
chatDB.addData(db,name,data);

the error after execution is as follows

that is, db is only valid within onsuccess