indexedDB中IDBDatabase對(duì)象已生成但不能調(diào)用createObjectStore方法創(chuàng)建命名空間，提示Uncaught TypeError: Cannot read property 'createObjectStore' of undefined。下面是代碼    var request = indexedDB.open("jusing"),        db;        user = {            username: "jusing",            age: 18,            gender: "male",            handsome: true        }    request.onsuccess = function() {        db = event.target.result;    }    var store = db.createObjectStore("users", {keyPath: "username"});    store.add(user);