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Is there an easy way to manage offline data with a web app, and synchronize with a server when there is a connection? I have been looking at Meteor, CouchDB and the likes, but still not sure what would be the least painfull way.

I could of course implement it myself with sockets or something similar, but if something is already made for the purpose, I don't see a reason to do it again.

I'm planning to work with Node as the server.

Thanks

danielsvane
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  • There is a module called now.js that was designed for a similar purpose, but the project has been abandoned now (despite how useful it may have been). http://news.ycombinator.com/item?id=4667826 – Anderson Green Dec 31 '12 at 05:08

2 Answers2

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You're talking about two things; 1) How to store/persist data if/when offline (storage mechanism), and 2) How to synchronize with a server when online (communication mechanism). The answer to 1 is some kind of local storage, and there any several ways of doing that (localstorage, websql, filesystem APIs etc) depending on your platform. The answer to 2 really depend on how urgent your synchronization needs are, but in general you can use HTTP itself with periodic (long-) polling, websockets and similar.

On top of both storage and communication mechanisms there are numerous libraries that make the job simpler, like Meteor (communication) and CouchDB (storage), but also many many more. There are even libraries that take care of the actual synchronization mechanism (with possible conflict resolution as well), but this very much depends on your actual application.

Updated: This framework looks promising, but I haven't tested it myself:

http://blog.nateps.com/announcing-racer-experimental-realtime-model

Marius Kjeldahl
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  • I am aware of the many ways to do local storage, and also how to send and receive data. I'm asking whether anything already has been made, that takes care of all of this in a single package. I am seriously considering Meteor, but since it is so beta, I was wondering if anything similar is out there. Anything where I can "save" to a database on the client, and simply abstract from all the rest. – danielsvane May 31 '12 at 13:48
  • Searching here for "html5 offline sync" turns up quite a few answers that discusses techniques, but very little in terms of ready-to-use solutions. It may very well be that "easy" and "solves all usecases" may be mutually exclusive, so it all depends on exactly what your use case is (one-way sync, two-way sync, one to one, one to many, many to many). – Marius Kjeldahl May 31 '12 at 14:05
  • Thanks for your help. I did some testing, and Meteor apparently works exactly as I want. When offline, the app continues to work as normal, and just treats the server as being very slow. When it regains connection it syncs all the data. – danielsvane May 31 '12 at 14:43
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You might want to look at cloud services as well. These are best if you are developing a new application as they push you more to a serverless model, and of course you have to be happy using a service.

Simperium () is an interesting cloud service - the only one I can find today that does syncing (unlike Firebase and Spire.io who are similar in other respects), and for iOS it includes offline storage, while for JavaScript clients you'd need to cover the local storage yourself using HTML5 features. Backbone.js seems to have some support for this, and Simperium can integrate with Backbone, using a similar API style.

For non-cloud services, Derbyjs () is an open source project that includes Racer, a data synchronization library (mentioned by the earlier answer) - both are under rapid development and not yet complete, but look interesting if your timescales allow, and don't require a cloud service. There is a comparison of Derbyjs to Meteor that is useful - although it's written by the Derbyjs developers it's not too biased.

I also looked at CouchDB, which has some interesting built-in replication features, but I didn't like its use of indexes that are updated lazily when a query needs them (or by a batch process), and I wasn't happy with exposing the server DB directly to clients to enable replication/sync. Generally I think it's best to decouple the client side local storage from the server side DB, and of course for a web app it would be hard to use CouchDB on the client.

RichVel
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