我找到了一个发送JSON文件的解决方案，其中XMLHttpRequest自动转换为indexedDB objectStore：

function sendData(pTable,pMess) {

var xhttp = new XMLHttpRequest();
var sendArray=[];
var request = indexedDB.open("dbapp",1, "persistent");
   
request.onsuccess = function (evt) {

    var db = request.result;
    var tx = db.transaction(pTable,"readwrite");
    var store = tx.objectStore(pTable);            
    var cursorRequest = store.getAll();
        
    cursorRequest.onsuccess = function(event) {
        var cursor=event.target.result;
 
        for(var item of cursor) {
            
          sendArray.push(item);

        };

        xhttp.open("POST", "../php/sincDATI.php", true);
        xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        xhttp.onreadystatechange = function() {
            if (this.readyState == 4 && this.status == 200) {
                $("#lblMessaggi").html("OK!"+ xhttp.responseText);
                    
            };
            
        };

        xhttp.send("pArr="+JSON.stringify(sendArray));

    };
};

};