javascript - 在 JavaScript 中使用异步 AJAX 请求管理异步 IndexedDB

Question

如何等待 IndexedDB 中的 AJAX 响应完成。我有以下代码，如果我异步运行它，第二个事务会将所有响应链接到第一个响应中的最后一项。我希望在登录时从服务器填充报告和收据存储，这样我就可以在需要时离线工作。如果我使其同步，它可以正常工作，但从用户体验方面来看，这很糟糕，因为应用程序有点卡住，所以我想避免这种情况。有人有建议吗？

var DBRequest = window.indexedDB.open(IDBName, IDBVersion);
DBRequest.onerror = function(event) {
    console.log("error: ");
};

DBRequest.onsuccess = function(event) {
    var response = DBRequest.result;
    SExpenses.removeAll();
    var z=0;
    Ext.Ajax.request({
        url:App.url.expenses,
        method: 'GET',
        async:true,
        params: {
            user_guid: App.user.guid,
            limit: 25
        },
        success: function(res){
            var result = Ext.decode(res.responseText);
            var dataIDB = response.transaction(["ReportDataLocal"],'readwrite').objectStore("ReportDataLocal");
            dataIDB.clear();
            var receiptIDB = response.transaction(["ReceiptsLocal"],'readwrite').objectStore("ReceiptsLocal");
            receiptIDB.clear();

            var savedID, savedRecID;

            Ext.each(result.data, function(item){

                z++;
                SExpenses.insert(0,item);
                var newObject = response.transaction(["ReportDataLocal"], "readwrite")
                .objectStore("ReportDataLocal")
                .add({DESCRIPTION: item.DESCRIPTION, BILLING_QTY: item.BILLING_QTY,
                      TRAVEL_EXPENSES: item.TRAVEL_EXPENSES,REQUEST_TYPE_ID: item.REQUEST_TYPE_ID, 
                     SERVER_ID: item.SERVER_ID
                     });

                newObject.onsuccess = function(event){

                    savedID = event.target.result;
                    SExpenses.findRecord('SERVER_ID',item.SERVER_ID).set({ID:savedID});
                    Ext.Ajax.request({
                        url: App.url.receipts,
                        async: true,
                        method: 'GET',
                        params: {
                            Request_Log_RC: item.SERVER_ID
                        },
                        success: function(retrieve){

                            var result2 = Ext.decode(retrieve.responseText);

                            Ext.each(result2.data,function(item2){
                                SReceipt.add(item2);
                                var newReceiptIDB = response.transaction(["ReceiptsLocal"],'readwrite')
                                .objectStore("ReceiptsLocal");

                                newReceiptIDB.add({EXPENSE_AMOUNT: item2.EXPENSE_AMOUNT, EXPENSE_CURRENCY_ID:item2.EXPENSE_CURRENCY_ID,
                                                   EXPENSE_NAME: item2.EXPENSE_NAME, REPORT_ID: savedID, CURRENCY_ABB: item2.CURRENCY_ABB,
                                                   EXPENSE_IMAGE: null, SYNCED: true, DELETED: item2.DELETED,
                                                   SERVER_ID: item2.SERVER_ID, SERVER_REPORT_ID: item.SERVER_ID,
                                                   EXPENSE_EXCHANGE_RATE: null
                                                  });
                                newReceiptIDB.onsuccess = function(event){
                                    savedRecID = event.target.result;
                                    SReceipt.findRecord('SERVER_ID',item2.SERVER_ID).set({ID:savedRecID});

                                };   
                            });
                        }
                    });   
                };
            });   
        }
    });

};

Answer 1

所以你需要做的是绑定(bind)项目，https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

基本上，如果您曾经对多个项目进行异步调用循环，并且需要回调来保留原始调用的索引，则可以绑定(bind)索引并将其传入。

var returnData = [];
var a = 10;
for(var i = 0; i < a.length; i++) {
    someAysncCall(function(data){
         returnData[i] = data;
    }).bind(null, i);
}

这将使 i 保持在回调的范围内。

从您的代码看来，您希望项目保留在上下文中，因此如果您添加绑定(bind)到此

newObject.onsuccess = function(event){

                savedID = event.target.result;
                SExpenses.findRecord('SERVER_ID',item.SERVER_ID).set({ID:savedID});
                Ext.Ajax.request({
                    url: App.url.receipts,
                    async: true,
                    method: 'GET',
                    params: {
                        Request_Log_RC: item.SERVER_ID
                    },
                    success: function(retrieve){

                        var result2 = Ext.decode(retrieve.responseText);

                        Ext.each(result2.data,function(item2){
                            SReceipt.add(item2);
                            var newReceiptIDB = response.transaction(["ReceiptsLocal"],'readwrite')
                            .objectStore("ReceiptsLocal");

                            newReceiptIDB.add({EXPENSE_AMOUNT: item2.EXPENSE_AMOUNT, EXPENSE_CURRENCY_ID:item2.EXPENSE_CURRENCY_ID,
                                               EXPENSE_NAME: item2.EXPENSE_NAME, REPORT_ID: savedID, CURRENCY_ABB: item2.CURRENCY_ABB,
                                               EXPENSE_IMAGE: null, SYNCED: true, DELETED: item2.DELETED,
                                               SERVER_ID: item2.SERVER_ID, SERVER_REPORT_ID: item.SERVER_ID,
                                               EXPENSE_EXCHANGE_RATE: null
                                              });
                            newReceiptIDB.onsuccess = function(event){
                                savedRecID = event.target.result;
                                SReceipt.findRecord('SERVER_ID',item2.SERVER_ID).set({ID:savedRecID});

                            };   
                        });
                    }
                });   
            }.bind(null, item);

应该有效