Your browser, my storage

Complex applications need a persistent database to store, search and join data: until now a dedicated server was needed to do this, and no offline usage of the app was possible. With the introduction of HTML5 and the concept of localStorage and Web Databases, we don’t need an external server anymore: everything is stored within the user browser and thus the web app can be used offline as well as online.

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1. Your browser, my storage a new approach on data storing (v.1.3) Francesco Fullone ff AT ideato.it
2. Who am I Francesco Fullone aka Fullo - PHP developer since 1999 - President - and Evangelist - CEO @ - founder @ - Nerd and geek
4. What we want is a lot of storage space, on the client, that persists beyond a page refresh and isn’t transmitted to the server. ~ M. Pilgrim
5. Persistent local storage is one of the areas where client applications traditionally win against web applications.
6. A jump in the past
7. Cookies were introduced in HTTP/1.0, limited to only 20 per domain and 4KB each. http://qrurl.it/r/3l
8. Cookies are sent to and from client at any connection. http://qrurl.it/r/3m
9. Microsoft with Internet Explorer 6 introduced dHTML and the userData API to store up to 64KB of data
10. Mozilla introduced with Firefox 2 the DOM Storage API, it will then know as Web Storage.
11. In 2002 Adobe created the Flash Cookies aka “Local Shared Objects” for Flash 6 Data storage increased to 100KB but it was difficult to be used
12. With Flash 8, in 2006, Adobe introduced the ExternalInterface to allow Js to access to the stored resources.
13. Between 2005 and 2007 dojox.storage was written by Brad Neuberg as a Js->Flash bridge to manage bigger chunks of data (with user prompt over 1MB).
14. Google created Gears in 2007, that introduced a database paradigm (based on SQLite) to solve the storage problem.
15. BUT
16. All these storage systems had different APIs, a common platform is needed by all the browser vendors.
18. The two approaches of storing: Application Cache Offline storage
19. Application Caching involves saving the application's core logic and user-interface. http://qrurl.it/r/3g
20. It is enabled by a file .appcache that declares which resources have to be saved locally. (theoretically limited to 5MB).
21. CACHE MANIFEST # Explicitly cached entries CACHE: index.html stylesheet.css images/logo.png http://www.anothersite.com/scripts/main.js # Resources that require the user to be online. NETWORK: login.php /myapi http://api.twitter.com # static.html will be served if main.php is inaccessible # offline.jpg will be served in place of all images in images/large/ FALLBACK: /main.php /static.html images/large/ images/offline.jpg .avi images/offline.jpg
22. applicationCache can use events to trigger application behavior window.applicationCache.onchecking = function(e) { log("Checking for application update"); }
23. applicationCache can use events to trigger application behavior/2 – SetInterval( function () { window.applicationCache.update(); }, 3600000 ); – window.applicationCache.addEventListener( 'updateready', function(){ window.applicationCache.swapCache(); }, false );
24. applicationCache or check if the browser is online If (window.navigator.onLine) { log("Application is online"); }
25. Chrome/Chromium doesn't support window.navigator.onLine attribute and... It doesn't have a real offline mode!
26. As stated in the specs: “window.navigator.onLine is inherently unreliable. A computer can be connected to a network without having Internet access.”
27. If you change a resource and you don't update (!=rev) the .appcache file the browser may not download the new file! (yes! cached resources have priority on the online ones)
28. Approaches to Data Storage
29. Data storage is about capturing specific data, or resources the user has expressed interest in. http://qrurl.it/r/3n
30. Web Storage is the simpler implementation of the Data Storage paradigm. http://qrurl.it/r/3h
31. Web Storage is based on a structure of key-value pairs like any JavaScript object. localStorage.setItem("bar", foo);
32. Web Storage can save up to 5MB but only as strings. So we have to force a casting if needed. var bar = parseInt(localStorage["bar"]);
33. Web Storage should be local based or session based. var bar = localStorage["bar"]; var foo = sessionStorage["foo"];
34. sessionStorage mantains a storage area that's available for the duration of the web session. Opening a new window/tab will create a new session.
35. localStorage relies only on client, so we have to track changes and use storage.events to sync server and client if needed.
36. localStorage lock the browser, do not save 5Mb every 5 seconds ;).
37. Web SQL Database is WAS just an offline SQL implementation, based on SQLite. http://qrurl.it/r/3i
38. this.db = openDatabase('geomood', '1.0', 'Geo', 8192); this.db.transaction(function(tx) { tx.executeSql("create table if not exists checkins(id integer primary key asc, time integer, latitude float, longitude float, mood string)", [], function() { console.log("siucc"); } » ); });
39. Web SQL Database is not supported by Microsoft and Mozilla, it is on browsers based on webkit.
40. But ... Web SQL Database is dead! as being dropped by W3C from 18/11/10 why bother more?
41. Web SQL Database is the only database storage engine that works on mobile devices!
42. IndexedDB is a nice compromise between Web Storage and Web SQL Database. http://qrurl.it/r/3j
43. IndexedDB allows to create an index on a certain field stored in a standard key->value mapping.
44. IndexedDB is promoted by all browsers vendor, but is not yet fully supported by all Firefox 4, Chrome 11, have full implementation. Safari 5.1 and IE 10 will have
45. var indexedDB = window.indexedDB || window.webkitIndexedDB || window.mozIndexedDB || window.OIndexedDB || window.msIndexedDB, IDBTransaction = window.IDBTransaction || window.webkitIDBTransaction || window.OIDBTransaction || window.msIDBTransaction; Using IndexedDB/1
46. var dbVersion = 1; var request = indexedDB.open("MyDb", dbVersion); request.onsuccess = function (event) { console.log("creating/accessing IndexedDB db"); db = request.result; } Using IndexedDB/2
47. var transaction = db.transaction(["todo"], IDBTransaction.READ_WRITE); var store = transaction.objectStore("todo"); var data = { "text": “text to be saved”, "timeStamp": new Date().getTime() }; var put = store.put(data); Using IndexedDB/3
48. // Get everything in the store; var keyRange = IDBKeyRange.lowerBound(0); var cursorRequest=store.openCursor(keyRange); cursorRequest.onsuccess = function(e) { var results = e.target.result; if(!!results == false) return; /* DO SOMETHING */ results.continue(); }; Using IndexedDB/4
49. indexedDB runs in its own thread! No browser locking!
50. FileAPI allows to manipulate file objects, as well as programmatically select them and access their data. http://qrurl.it/r/3k
51. File API includes FileReader and FileWriter APIs. Actually is supported by Chrome, Firefox > 3.6, Safari > 5.1, Opera > 11.1.
52. filer.js http://qrurl.it/r/c3 webFS.js http://qrurl.it/r/c4
53. First steps on offline storage development. http://flic.kr/p/5PnRQr
54. Storages Status/1
55. Storages Status/2
56. Storages Status/3
57. Detect if the storing feature is supported by the browser (with modernizr), otherwise degradate to something else. (ie. dojox.storage)
58. Use libraries that manage data for you (ie. storagejs, lawnchair)
59. Protect against lost data, sync automatically. http://qrurl.it/r/3o
60. Automatically detect when users are online. http://qrurl.it/r/3p
61. Do not exceed in storing data, you can store binary data base64 encoded but remember the pitfalls in performance.
62. Avoid race conditions. If possible use WebSQL to use its transactions features.
63. use local storage to help your application to become faster.
64. basket.js http://qrurl.it/r/c2
65. basket .require('jquery.js') .require('underscore.js') .require('app.js').wait(function(){ • /* do something cool */ });
66. ?
67. via Quinto Bucci 205 47023 Cesena (FC) info AT ideato.it www.ideato.it Francesco Fullone ff@ideato.it @fullo