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Not able to retrieve object properties when looping through objects in indexedDB

I am not able to retrieve properties when looping through objects stored in indexedDB. When i attempt to get objects trough tasksStore.get(i);, i get the error Cannot read property 'property' of undefined at IDBRequest.getTasks.onsuccess, however, if I change it to tasksStore.get(1);, it works fine, and gets object with id=1 x index's length.
I've tried checking the typeof of both ways, and they both return number.
//success handler on connection
request.onsuccess = function(e) {
db = request.result;
//define store index
tasksStore = tasksTx.objectStore("tasksStore");
//error handler on result of the request
db.onerror = function(e) {
console.log("ERROR " + e.target.errorCode);
}
//variable for counting objects in the index
let amountOfTasks = tasksIndex.count();
//error handler
amountOfTasks.onerror = function() {
console.log("There was an error finding the amount of tasks")
}
//success handler
amountOfTasks.onsuccess = function() {
for (var i = 1; i < amountOfTasks.result; i++) {
let getTasks = tasksStore.get(i);
let getTasksElementContainer = document.getElementById("list-tasks");
let createTasksList = document.createElement("li");
createTasksList.id = "task-" + i;
getTasks.onerror = function() {
console.log("There was an error looping through the tasks")
}
getTasks.onsuccess = function() {
console.log(getTasks.result.title); //getTasks.result works, getTasks.result.title does not.
getTasksElementContainer.appendChild(createTasksList);
//JSON stringify to return object in string format, and not [Object object]
createTasksList.innerHTML = JSON.stringify(getTasks.result.title);
}
}
}
}

When you call IDBObjectStore.get with a key that doesn't exist in your database, the resulting value is undefined. That likely explains why sometimes getTasks.result is undefined.
If you're still having trouble, you'd likely be well served by making a self-contained reproducible example. You'll probably find your own bug in the process of doing that. If not, it's easier to get more specific help on Stack Overflow if you have some code that other people can run to directly observe the problem (so including database creation and inserting data).

How do I submit an array from the client to a server (ExpressJs) using AJAX?

I'm working on a web application in which a user can drag and drop div elements, whose content is generated from a database, into their preferred order. I want the user to be able to, when they are finished arranging the divs, submit their list (in order) to the server and store the new order in a table. I'm using AJAX to do this, however I'm not sure if that is necessary/the proper way to do this, since I don't need to asynchronously update the page (I just need to submit the data). I've tried a variety of methods to get my array to the server in a usable format (it needs to be iterable and allow for element locations to be compared). I have tried using JSON.stringify/parse, creating a custom object, simply submitting the array on its own, and so on. Here is my code, the most relevant bits are towards the bottom by the makeRouteArray function. Ideally to accomplish this I would like to use just JavaScript (no jQuery). Finally, please excuse my messy code, I'm learning.
// get two groups of elements, those that are draggable and those that are drop targets
let draggable = document.querySelectorAll('[draggable]');
let targets = document.querySelectorAll('[data-drop-target]');
// div immediately surrounding bus routes
var busList = document.getElementById("bus-list");
const button = document.getElementById("button");
// store the id of the draggable element when drag starts
function handleDragStart(e) {
e.dataTransfer.setData("text", this.id); // sets 'text' value to equal the id of this
this.classList.add("drag-start"); // class for styling the element being dragged, sets opacity
}
function handleDragEnd(e) {
e.target.classList.remove('drag-start');
}
function handleDragEnterLeave(e) {
// should provide visual feedback to user?
}
// handles dragover event (moving your source div over the target div element)
// If drop event occurs, the function retrieves the draggable element’s id from the DataTransfer object
function handleOverDrop(e) {
e.preventDefault();
var draggedId = e.dataTransfer.getData("text"); // retrieves drag data (DOMString) for specified type
var draggedEl = document.getElementById(draggedId);
draggedEl.parentNode.insertBefore(draggedEl, this); // inserts element being dragged into list
var draggedArray = Array.from(draggedEl.parentNode.children); // creates new array which updates current location of each route
e.target.classList.remove('drag-start'); // sets opacity back to 1
// if (e.type === "drop") {
// // when dropped, update localstorage
savePage(draggedArray);
// }
}
// get each full bus-route div in #bus-list with p content as single arr item each
// called when item is dropped
function savePage(dArray) {
// honestly i can't remember what this does precisely
// but i can't seem to add to localstorage in the way i want without it
var arr = Array.prototype.map.call(dArray, function(elem) {
return elem.outerHTML;
});
localStorage.newList = JSON.stringify(arr); // have to stringify the array in order to add it to localstorage
}
// ideally it should just update the order of the bus routes to reflect local storage
// and add classes/ids to the divs etc. (hence using outerHTML)
function makePage() {
// getting the item from localstorage
var getData = localStorage.getItem("newList");
// parsing it back into an array
var parsedData = JSON.parse(getData);
// string to hold contents of array so they can be display via innerHTML
var fullList = "";
if (localStorage.getItem("newList") === null) {
return; // maybe this is wrong but if there's nothing in local storage, don't do anything
} else {
for (let i = 0; i < parsedData.length; i++) {
fullList = fullList + parsedData[i];
}
busList.innerHTML = fullList;
// reassigning targets after calling function in order to re-register event handlers
draggable = document.querySelectorAll('[draggable]');
targets = document.querySelectorAll('[data-drop-target]');
}
}
// probably better way to do this
for (let i = 0; i < draggable.length; i++) {
draggable[i].addEventListener("dragstart", handleDragStart);
draggable[i].addEventListener("dragend", handleDragEnd);
}
// drop target elements
for (let i = 0; i < targets.length; i++) {
targets[i].addEventListener("dragover", handleOverDrop);
targets[i].addEventListener("drop", handleOverDrop);
targets[i].addEventListener("dragenter", handleDragEnterLeave);
targets[i].addEventListener("dragleave", handleDragEnterLeave);
}
// rolling average: new_average_score = old_average_score * (total_users-1)/total_users + user_route_rank/total_users
// user id, column per route (score)
// session id
// submit button to save changes to db
// when submit is clicked
// get current results from either local storage or from currently ordered + displayed list
// data will be in array format
// do i need AJAX to be able to submit something other than form data to a server?
// is submitting data in this format (taken from page's HTML ordering) even possible?
// i'd prefer to not use jQuery
// how do i submit an array to the server (express) and then parse (?) it to make it useable?
// so far i have tried JSON.stringify/parse, making a custom object, just submitting array, etc.
// ultimately what i need is a data type that i can loop over and compare positions of stored elements
var makeRouteArray = function() {
var currentOrderArr = Array.from(busList.children);
var idData = currentOrderArr.map(function(el) {
return Number(el.id.slice(2));
});
return idData; // not sure if having two return statements like this is okay
};
button.addEventListener("click", function(e) {
var request = new XMLHttpRequest();
request.open('POST', '/submit', true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
request.send(data);
});
makePage();
The makeRouteArray function is taking ids from an HTML ul and stripping them of the first two characters because I only want to use the numbers (the ids are structured as #r-num). An array of these numbers is what I would like to submit to the server and if possible, once on the server, return the JSON object to an array.
Thanks!

How to dynamically create and populate multiple objectStores on HTML5 IndexedDB in the same transaction?

Working on the IndexedDB API, I'm creating many objectStores that belong to the same database, in one transaction, when the user loads a webpage.
I order to do so, I created an object which contains many objectStores to be created, each one has it's name, data and index.
Then a function runs the object and effectively creates Database, objectStores and indexes for each one.
However of all OS's created, just the last member of the object gets populated. Say of 5 objects to be created and populated, 5 are created but only the last one is populated.
Clearly is a problem of overwriting or some issue related to the JS stack or asynchronicity.
I appreciate any help to make the code populate all OS not the last one.
My browser is Chrome 56, I fetch data from an API whose response is OK, and I'm coding on vanillajs. I appreciate your help in vanillajs, there is no way to use any library or framework different from what the modern Web Platform offers.
Here is the code:
On the HTML side, this is an example of the object:
var datastores = [{osName:'items', osEndpoint: '/api/data/os/1/1', osIndex:'value'}, {osName:'categories', osEndpoint: '/api/data/os/2/1', osIndex: 'idc'}];
On javascript:
var request = indexedDB.open(DB_NAME, DB_VERSION); // open database.
request.onerror = function (e) { // error callback
console.error("error: " + e.target.errorCode);
};
request.onupgradeneeded = function (e) { // the onupgradeneeded event which creates all schema, dataabase, objectstores and populates OS.
var db = this.result;
for (var i in datastores) { // loop the objectStore object.
var objectStore = db.createObjectStore(datastores[i].osName, {keyPath: "id"});
TB_NAME = datastores[i].osName; // instantiate each objectStore name.
objectStore.createIndex(datastores[i].osIndex, datastores[i].osIndex, { unique: false }); // create each index.
objectStore.transaction.oncomplete = function(e) { // oncomplete event, after creating OS...
fetchGet(datastores[i].osEndpoint, popTable); // runs a function to fetch from a designated endpoint and calls a function.
};
}
}
Now the functions: to fetch data and to populate data:
function fetchGet(url, function) { // fetch from API.
fetch(url, {
method: 'GET'
}).then(function(response) {
return response.json();
}).then(function(json) {
popTable (json);
}).catch(function(err) {
console.log('error!', err);
});
}
function popTable(json) {
var m = 0;
var tx = db.transaction(TB_NAME, "readwrite");
tx.oncomplete = function(e) {
console.log("Completed Transaction " + TB_NAME);
};
tx.onerror = function(e) {
console.error("error: " + e.target.errorCode);
};
var txObjectStore = tx.objectStore(TB_NAME);
for (m in json) {
var request = txObjectStore.add(json[m]);
request.onsuccess = function (e) {
console.log('adding... ' );
};
}
}

The for (var i in datastores) loop runs synchronously, updating the global TB_NAME variable every time. When the loop finishes, TB_NAME will be holding the name of the last object store.
By the time the asynchronous popTable calls run, TB_NAME will forever be holding the name of the last store, so that's the only one that will update. Try adding logging to popTable to see this.
You'll need to pass the current value of the store name along somehow (e.g. as an argument to fetchGet). Also note that although you pass popTable as a parameter when calling fetchGet you're not actually accepting it as an argument.
...
Specific changes:
Change how you call fetchGet to include the store name:
fetchGet(datastores[i].osEndpoint, popTable, datastores[i].osName);
Change the fetchGet function to accept the args:
function fetchGet(url, func, name) {
And then instead of calling popTable directly, do:
func(json, name);
And then change the definition of popTable to be:
function popTable(json, name) {
... and use name in the transaction.

How to check if key is not found in IndexedDB?

On the indexeddb i want to look if there is a key permanent and do some actions. But if not, i want to make some other actions. I can do the actions if the permanent is there, however when it is not I can get the onerror to work. Is the onerror suppose to do this thing? How can I check if there is not value in it?
var hashtype = 'permanent';
var getPermanent = store.get(hashtype);
getPermanent.onsuccess = function() {
var ivrame = getPermanent.result.value;
};
getPermanent.onerror = function() {
console.log('onerror')
};

See the note under https://w3c.github.io/IndexedDB/#dom-idbobjectstore-get - the get method yields success with undefined if there is no matching record.
So you have a few options:
Use get(key) and test the result for undefined. This works unless undefined is a value you expect to store (it's a valid value)
Use count(key) - the result will be 1 if present, 0 if absent. Easy if you're just testing for existence, but doesn't get you the record.
Use openCursor(key) and test to see if the request's result is a cursor (record present as request.result.value) or undefined (no record in range)
For your code:
var hashtype='permanent';
// #1: Use get
var getPermanent = store.get(hashtype);
getPermanent.onsuccess = function() {
if (getPermanent.result === undefined) {
// no record with that key
} else {
var value = getPermanent.result;
}
};
// #2: Use count
var getPermanent = store.count(hashtype);
getPermanent.onsuccess = function() {
if (getPermanent.result === 0) {
// no record with that key
} else {
...
}
};
// #3: Use cursor
var getPermanent = store.openCursor(hashtype);
getPermanent.onsuccess = function() {
var cursor = getPermanent.result;
if (!cursor) {
// no record with that key
} else {
var value = cursor.value;
}
};

The function assigned to request.onsuccess is a callback function that is always called, regardless of whether the value is present in the store. When there is no corresponding object in the store, the result object will be undefined. When there is a corresponding object in the store, the result object will be defined. So you simply need to check if the object is defined from within the onsuccess callback function.
request.onerror is a separate callback from request.onsuccess. onerror gets called when there is some type of failure in indexedDB (e.g. something like you tried to get a value from a store that doesn't exist, or you tried to put a duplicate object into a store that doesn't permit duplicates). request.onerror does not get called when no value is found as a result of calling store.get, because that is not considered an 'error' in the failure sense.
So, what you want to do is something like this:
var hashtype='permanent';
var getPermanent = store.get(hashtype);
getPermanent.onsuccess = function(event) {
//var ivrame=getPermanent.result.value;
var result = getPermanent.result;
if(result) {
console.log('Got a result!', result);
var ivrame = result;
} else {
console.log('Result was undefined! No matching object found');
}
};
getPermanent.onerror = function() {
console.log('Something went wrong trying to perform the get request');
};
Do not try and access request.result.value. There is no such thing in the case of a get request. When using store.get, request.result contains the matching object you want, or is undefined. When using store.openCursor, request.result contains the cursor, which is defined if there is at least one matching object and you have not already iterated past it. To get the matching object at the cursor's current position, you would use cursor.value. Here, cursor.value will always be defined, because cursor would otherwise be undefined, and you would obviously check for that beforehand.

Instead of using getPermanent.result to access data provided by 'get' request it is better to use event.target.result. It also can be compared with undefined to check absence of requested key:
db = this.result;
var tr = db.transaction("data");
var objstore = tr.objectStore("data");
var getres = objstore.get(0);
getres.onsuccess = function(event)
{
if(event.target.result.data === undefined)
console.log("key not found");
}

IndexedDB DOM IDBDatabase Exception 11 even after using oncomplete

I am very new to IndexedDB Concepts. I am trying to Store a list of movies in the IndexedDB and retrieve it. But for some reason when i try to retrieve it there is a DOM IDBDatabase Exception 11 in chrome browser. I try to retrieve it by using a simple alert. I also tried to retrieve the data by putting the alert inside an onComplete event, but this too seems to be a failure. Could someone please let me know what wrong i am doing. Below is my code.
const dbName = "movies";
var request = indexedDB.open(dbName, 1);
request.onerror = function(event) {
alert("Seems like there is a kryptonite nearby.... Please Check back later");
};
request.onsuccess = function(event) {
var db = event.target.result;
var transaction = db.transaction(["movies"],"readwrite");
var objectStore = transaction.objectStore("movies");
var request1 = objectStore.get("1");
request1.result.oncomplete=function(){
alert("The movie is"+request1.result.name);//This is the place where i get the error
}
};
request.onupgradeneeded = function(event) {
db = event.target.result;
var objectStore = db.createObjectStore("movies", { keyPath: "movieid" });
objectStore.createIndex("name", "name", { unique: false });
objectStore.createIndex("runtime", "runtime", { unique: false });
for (var i in movieDataToStore) {
objectStore.add(movieDataToStore[i]);
}};

I still do not know what was wrong with the last program. i re-wrote the above program and it worked like a charm. here is the code. Hope this helps anyone who is stuck with this problem. Also if anyone figures out what went wrong the last time please share your thoughts.
var db; //database will be stored in this value when success is called
var movieDataToStore = [{ movieid: "1", name: "Keep my Storage Local", runtime:"60"},
{ movieid: "2", name: "Rich Internet Conversations", runtime:"45"},
{ movieid: "3", name: "Applications of the Rich and Famous", runtime:"30"},
{ movieid: "4", name: "All Jump All eXtreme", runtime:"45"}];
window.query = function() {
db.transaction("movies").objectStore("movies").get("1").onsuccess = function(event) {
alert("QUERY: CThe first movie is" + event.target.result.name);
};};
window.onload = function() {
if (!window.indexedDB) {
window.alert("Your browser doesn't support a stable version of IndexedDB. Such and such feature will not be available.")
}
else{
var request = indexedDB.open("movies", 1);
request.onerror = function(event) {
alert("Seems like there is a kryptonite nearby.... Please Check back later");
};
request.onsuccess = function(event) {
db = this.result;
query();
};
request.onupgradeneeded = function(event) {
var db = event.target.result;
if(db.objectStoreNames.contains("movies")) {
db.deleteObjectStore("movies");
}
var objectStore = db.createObjectStore("movies", { keyPath: "movieid"});
objectStore.createIndex("name", "name", { unique: false });
objectStore.createIndex("runtime", "runtime", { unique: false });
for (var i in movieDataToStore) {
objectStore.add(movieDataToStore[i]);
}
};
}
};

I think it is bad practice to insert data in the onupgradeneeded context. You should be doing this separately in an unrelated function at some other time. In fact, attempting to insert the data on a database whose version was incremented since last page load will automatically trigger the upgradeneeded event for you.
While many of the online examples shove the database connection handle (your db var) into some global scope variable, this is also a bad practice that will lead to errors down the road. Only access the db var within your callbacks as a parameter. In other words, your openRequest.onsuccess function should pass the db variable to the query function. This also reduces the chances of any garbage collection issues later and leaving database connections open (which the designers of indexedDB allow for, but should generally be avoided).
If your movie ids are integers, it isn't clear to me why you are storing and retrieving them as strings. You can store integer values. You can pass an integer to store.get.
You are using for...in inappropriately. It will work, but for...in is intended for looping over the keys of object literals (like var x = {key:value}). Use a normal for loop or use array.foreach when iterating over your movies array.
As you found out in your fixed code, it is better to use request.onsuccess and request.onerror. There is also a transaction.oncomplete. But I am not sure there is a request.oncomplete. What happens is you are setting the oncomplete property of an IDBRequestObject but this does nothing since the code never triggers it.
DOM 11 usually signals you tried to access a table that does not exist or is in an incorrect state. Usually this happens due to mistakes elsewhere, like onupgradeneeded never getting called when connecting. It is confusing, but given the way your code is setup, basically the db gets created the first time your page loads, but then never gets created again, so while developing, if you made changes, but do not increment your db version, you will never see them.