javascript - IndexedDB 引用错误 : db is not defined

Question

我正在尝试为 Firefox OS 创建一个应用程序，它基本上需要使用 IndexedDB 存储一些数据。

当用户点击提交按钮时调用 store() 函数，这会导致创建用户提交表单的名称和描述变量。

但是，我不断收到引用错误，提示我的数据库对象未定义。知道为什么会这样吗？

这是我当前的代码:-

function store () {
    // create the transaction with 1st parameter is the list of stores and the second specifies
    // a flag for the readwrite option
    var transaction = db.transaction([ 'Apps' ], 'readwrite');

    //Create the Object to be saved i.e. our App details
    var value = {};
    value.name = name;
    value.desc = description;

    // add the details to the store
    var store = transaction.objectStore('Apps');
    var request = store.add(value);
    request.onsuccess = function (e) {
        alert("Your App data has been saved");
    };
    request.onerror = function (e) {
        alert("Error in saving the App data. Reason : " + e.value);
    }
}


$(document).ready(function(){
// variable which will hold the database connection
var db;

    if (window.indexedDB) {
        console.log("IndexedDB is supported");
    }
    else {
        alert("Indexed DB is not supported!");
    }

    // open the database
    // 1st parameter : Database name. We are using the name 'Appsdb'
    // 2nd parameter is the version of the database.
    var request = indexedDB.open('Appsdb', 1);

    request.onsuccess = function (e) {
        // e.target.result has the connection to the database
        db = e.target.result;

        console.log(db);
        console.log("DB Opened!");
    }

    request.onerror = function (e) {
        console.log(e);
    };

    // this will fire when the version of the database changes
    // We can only create Object stores in a versionchange transaction.
    request.onupgradeneeded = function (e) {
        // e.target.result holds the connection to database
        db = e.target.result;

        if (db.objectStoreNames.contains("Apps")) {
            db.deleteObjectStore("Apps");
        }

        // create a store named 'Apps'
        // 1st parameter is the store name
        // 2nd parameter is the key field that we can specify here. Here we have opted for autoIncrement but it could be your
        // own provided value also.
        var objectStore = db.createObjectStore('Apps', { keyPath: 'id', autoIncrement: true });

        console.log("Object Store has been created");
    };

});

Answer 1

问题在于 db 变量的范围。当前，您在 $(document).ready 函数中声明了以下行 var db;。将其声明移至更全局的范围，即在此函数之外，并且该变量也将在 store() 函数中可见。

希望这对您有所帮助。