How can I access indexedDB synchronously?

Question

The indexedDB has a spec saying that you can access an indexed database synchronously, but it hasn't been implemented yet.

I was just wondering if there is a way to make it synchronous manually,

My JavaScript looks like this,

var trans = databaseAsync.transaction(["mapTile"], IDBTransaction.READ_WRITE);
var store = trans.objectStore("mapTile");
var keyRange = IDBKeyRange.bound(evt.data[0], evt.data[0]);
var cursorRequest = store.openCursor(keyRange);

// can you put some kind of wait in here?

cursorRequest.onsuccess = function(e)
{
    var result = e.target.result;
    if(!!result == false)
    {
    }
}

So can you put something in there to make it wait until the onsuccess method has been called before continuing on?

The reason why I want to do this is the code above is wrapped inside this method,

dojo.extend(esri.layers.ArcGISTiledMapServiceLayer, {
      getTileUrl : function(level, row, col)
      {
          // blah
          return url;
      }

So it is an ESRI tile layer (which will load tiles onto a map on my web page), and that method needs to return the url straight away for a particular tile. It will either be a URL to load the image from if it isn't cached in the database already, or this,

data:image;base64,*BASE64DATA*

Where BASE64DATA is the data from the database if previously cached.

I was previously using the localStorage for this, which works synchronously, but that has a 5MB limit so I thought I would experiment with indexedDB.

6 year 4 months later...this question still holds value and looks for a decent updated answer!! — NoobEditor, Jun 26 '18 at 04:39

score 3 · Answer 1 · answered Aug 29 '12 at 13:31

IndexedDB Sync API is marked as a risky part of the IndexedDB specification and they might be removed due to potential lack of implementations.

I've implemented 'sync' solution using the 'oncomplete' transaction event which guaranties that the current action is finished before starting the next one, and I also use custom semaphore and queue logic which handles the async calls from GUI and ensures that 2 open connections towards IndexedDB database won't happen at the same time.

Is the code for what you described in this post available anywhere? — dumbmatter, Aug 29 '12 at 14:45

score 3 · Answer 2 · edited May 23 '17 at 11:46

3

An elegant way of doing this is provided in the accepted answer to this question I asked a couple months ago. Unfortunately, it relies on feature of JavaScript 1.7 (generators) that is only supported in Firefox. Hopefully some day this technique will be more widely supported.

edited May 23 '17 at 11:46

Community

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answered Aug 29 '12 at 14:44

dumbmatter

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score 2 · Answer 3 · edited May 23 '17 at 12:09

2

There is a more general question how to wait for asynchronous functions where you will find an answer: How to block on asynchronous functions in JavaScript

I also found a nice waitFor routine inside Trial Tool.

edited May 23 '17 at 12:09

Community

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answered Feb 26 '12 at 10:25

toka

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score 0 · Answer 4 · edited Aug 13 '12 at 17:40

0

IE10 supports the sync api, but the indexeddb sync api can only be used inside a web worker. If you are working in the UI thread you need to use the async API.

Easiest way to work with the async API is through promises.

edited Aug 13 '12 at 17:40

Dan D.

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answered Aug 13 '12 at 06:12

Kristof Degrave

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Please [don't add signatures or taglines to your posts](http://stackoverflow.com/faq#signatures). – user229044 Aug 13 '12 at 16:04

How can I access indexedDB synchronously?

4 Answers4

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