With HTML5's offline capabilities is it possible to create an app that will persist after the connection is lost and the browser is closed? Specifically, here's what I'd like to do:
Connect to the app while online. Download the entire app including a small database it runs on.
Close the browser and disconnect.
Open the browser again while offline and load the app from the local cache.
Thanks to Mark Pilgrim's excellent book I believe I have an idea of how to accomplish the first step, I'm mainly wondering if the last step is possible. If this is possible, I'm guessing it requires some configuration of the browser. Any settings I should be aware of that aren't obvious?
Thanks very much for any help offered.
The last step should be possible - it just depends on what extent you want to implement it to. To my knowledge it shouldn't require any browser settings. You just have to be aware of the limitations of local storage, which I believe is 5mb max at the moment (for most browsers). Obviously you'd have to perform the checks for such permissions as outlined int the Dive Into Html5 guide you linked.
The quickest and dirtiest way is to simply issue a GET request to your online app. If it responds correctly, then use the online version. If not, use the local cache. Just disguise the timeout/failed response as a 'loading' screen.
Related
I know that the most Iconic feature of PWA are
Service Worker: which make user can use the app offline from cached resources
Add To Home Screen: With this feature, user can add a shortcut of the app on their mobile home screen, to get a experience like interacting with a Native App(But there still a huge different, in my opinion)
etc.
However, I can do like all of them on about 6/7 years ago by using the HTML5 technology at that time, I know that service worker comes recently but there also was "HTML5 App Cache, as well as the Local Storage, Indexed DB, and the File API specifications." can do similar things.
Is there anyone can explain what's the difference between PWA and HTML5 webapps? or they are just the in term of same? or a similar concept but different implementation? or PWA is the (next gen/extension) of HTML5 webapp?
I might have some misunderstanding on PWAs, since I am new to this term, Thanks.
If keep it simple PWA is ordinary site with 3 additional features.
responsive design - site should look well on all devices
manifest.json - site must have general description about itself stored in manifest.json
caching - site must work offline
I believe 1 and 2 is easey. And 3 is realy what PWA is all about. So the question is: how we can provide offline support?
First problem is how we can get our initial .html .css and .js files without internet connection? Answer is: we should use service worker or App Cache. But App Cache has a lot of problems and probably will be deprecated, in other hand service worker under developement and become better each month. You can read more about their difference here.
Second problem is how we can get server data without internet connection? We should store most vital data somwhere. But after we get our .js file from cache we have access to Local Storage, Indexed DB etc. So we can store vital data in any of this storage while we online and get it back from them when we offline. It is totally up to you how you will handle that.
I believe there no cleare and strict defentiton for PWA and HTML5 webapp (at least for now). So you can asume it is the same but today PWA is more common word.
I am about to start, working on a offline web application using HTML5, indexed db.
I have been reading a lot about it. But I got little confused thinking if the user deletes the cache of the browser, my app cache would also got deleted. And then there would be no way to use the application offline, until we got connected to internet, and browser creates a fresh cache.
Is this assumption true..or Is there a way to protect the app cache from getting deleted accidentally.
No. There isn't.
This is a normal behaviour which is similar to mobile apps. If users've removed their native apps, they need to redownload them whenever they want to reuse those apps. Appcache is not a silver bullet for the case.
I have an HTML5/jquery mobile web app at http://app.bluedot.mobi. It is used for long distance races to track competitors via SPOT satellite tracking. The issue I have not yet resolved is that when loading the app when no data connection exists, the browser throws a "no data connection" alert popup as it is attempting to fetch the manifest during the checking event. Even when a data connection is present, loading the app can take a very long time. There are ~ 500 files to check. The fastest way to load the app (from a phone) is to be in airplane mode and dismiss the browser's alert - not so elegant.
Rather than force an update on users who tend to be in the backcountry with a spotty connection, I want to use applicationCache.update() programmatically, giving the user control over the process and speeding up app load whether on or offline.
Is this currently possible with the HTML5 spec and respective browser implementations?
Sounds like you need the abort() method. Unfortunately it is very new, and it will probably be a while before it is implemented by the majority of mobile browsers.
There are ~ 500 files to check.
It sounds like you're implying that the browser checks each file to see if there's any of them which has changed. This is not correct. The browser only checks the manifest file if that has changed, and that is a simple byte check. If the manifest file has not changed, the browser believes nothing has changed.
So if your application is slow to start, it might be your because your application is complex and there's alot of HTML and Javascript to parse. I would advise you to take a look at the application and see if there's anything you can optimize. In that case, you might want to take a look at Yahoo's Best Practices for Speeding Up Your Web Site page.
For example, I noticed you have a lot of Javascript code in the HEAD section. The beforementioned article advices us to move all Javascript (To the extent of what's possible) to the bottom of the page, so that the browser can start rendering the page as soon as possible. And there's a lot of other sound advice in the article. So take a look, I'm sure you'll find it useful. :-)
With many browsers adding proper local storage support (and with this whole HTML5 buzz), there is a lot of talk about offline web apps competing with desktop software. But, as a matter of fact - one quick "clear private data" on your browser (which a lot of people do) - clears all the local storage data.
I'm now thinking that local storage in browsers can at best be used to cache data temporarily before being sync-ed with the web server, but truly offline web applications can't rely on HTML5's local storage permanently due to the problem I outlined above.
Is there a scope for offline web applications that actually depend on data extensively?
My take on this is that the offline capability of online web apps can compete with desktop software, but not pure offline web-apps.
Why? Well, the major drawback of online web apps was what happens when you lose your network connection when doing any work. Seeing as this can be resolved now, the competition is truly on. Imagine editing a document online, then move around without internet, come back online and then sync the changes and continue to work as if nothing happened. That is truly awesome.
For this to work, the browser should allow to store data in a location that you can pick which would mean access to OS layer, which will probably not happen anytime soon...
I have an HTML5 site. I want to do following thing:
Walk through files in a folder
Find all images
Get exif file from images
Analyze an exifs (on server)
Correct bad exifs
This is a best scenario, that it can be. I am conscious that 1st and 2second step is possibly done only by selecting this files by user. And 5th step is possible only when the analysis will be done at user's machine. So what is the best way to do it (to get closer as much to the optimal scenario)? What should I use without need to force a user to install anything?
EDIT:
At least I have used free GeckoFX web browser as a basic desktop app. Interface is created in HTML+JS Thx all
You would need to create an application that runs on the computer of the user. You can't create an HTML5 site that does this.
A Chrome HTML5 webapp should be able to do this.
I'm actually looking at this in these days.
Here is a NOT WORKING example ( due to old API specs, I think)
http://benno.id.au/blog/2009/12/30/html5-fileapi-jpegmeta
But should at least give some good insights.
You should use ExifTool.
It is available as a Perl library here:
http://www.sno.phy.queensu.ca/~phil/exiftool/ExifTool.html
And also as a command-line tool which can be ran by the server (same site).