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CHAPTER 6 STORING DATA IN THE BROWSERwindow.applicationCache.swapCache();window.location.reload(false);}});} else {createDialog("Try again later");}});});This is a simple change, and you’ll quickly realize that I am doing some mild misdirection. When thebrowser is online, the user can submit the form as normal, and any data in local storage is cleared. Themisdirection comes when the browser is offline and the user clicks the Save for Later button. All I do iscall the createDialog function, telling the user that the form data has been saved. However, I don’tactually need to save the data because I am using persistent observable data items in the view model.The user doesn’t need to know about this; they just get the benefit of the persistence and a clear signalfrom the web application that the form data has not been submitted. When the browser is online again,the user can submit the data. Using local storage all of the time means that the user won’t lose their dataif they close and later reload the application before being able to submit the form to the server. Forcompleteness, Listing 6-13 shows the createDialog function, which I defined in the utils.js file. This isthe same approach I used to create an error dialog in the original example, and I moved the code into afunction because I needed to create the same kind of dialog box at multiple points in the application.Listing 6-13. The createDialog Functionfunction createDialog(message) {$('' + message + '').dialog({modal: true,title: "Message",buttons: [{text: "OK",click: function() {$(this).dialog("close")}}]});};I have taken a very simple and direct approach to dealing with form data when the browser isoffline, but you can easily see how a more sophisticated approach could be created. You might, forexample, respond to the online event by prompting the user to submit the data or even submit itautomatically using Ajax. Whatever approach you take, you must ensure that the user understands andapproves of what your web app is doing.Storing Complex DataStoring name/value pairs is perfectly suited to storing form data, but for anything more sophisticated,such a simple approach starts to break down. There is another browser feature, called IndexedDB, whichyou can use to store and work with more complex data.156www.it-ebooks.info
CHAPTER 6 STORING DATA IN THE BROWSER• Note IndexedDB is only one of two competing standards for storing complex data in the browser. The other isWebSQL. As I write this, the W3C is supporting IndexedDB, but it is entirely possible that WebSQL will make acomeback or, at least, become a de facto standard. I have not included WebSQL in this chapter because supportfor it is limited at present, but this is an area of functionality that is far from settled, and you should review thesupport for both standards before adopting one of them for your projects.It is still early days for IndexedDB, and as I write this, the functionality is available only throughvendor-specified prefixes, signifying that the browser implementations are still experimental and maydeviate from the W3C specification. Currently, the browser that adheres most closely to the W3Cspecification is Mozilla Firefox, so this is the browser I have used to demonstrate IndexedDB.• Caution The examples in this chapter may not work with browsers other than Firefox. In fact, they may notwork even with versions of Firefox other than the one I used in this chapter (version 10). That said, you should stillbe able to get a solid understanding of how IndexedDB works, even if the specification or implementations change.The IndexedDB feature is organized around databases that, like local and session storage, areisolated on a per-origin basis so that they can be shared between applications from the same origin.IndexedDB doesn’t follow the SQL-based table structure that is common in relational databases. AnIndexedDB database is made up of object stores, which can contain JavaScript objects. You can addJavaScript objects to object stores, and you can query those stores in different ways, some of which Idemonstrate shortly.The result of this approach is a storage mechanism that is more in keeping with the style of theJavaScript language but that ends up being slightly awkward to use. Almost all operations in IndexedDBare performed as asynchronous requests to which functions can be attached so that they are executedwhen the operation completes. To demonstrate how IndexedDB works, I am going to create a CheeseFinder application. I will put the cheese product data into an IndexedDB database and provide the userwith some different ways of searching the data for cheeses they might like. Figure 6-2 shows the finishedweb app to help provide some context for the code that follows.157www.it-ebooks.info
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Contents at a Glance• About the A
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CHAPTER 1 GETTING READYWhat Do You
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C H A P T E R 2Getting StartedIn th
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CHAPTER 3 ADDING A VIEW MODELCreat
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C H A P T E R 4Using URL RoutingIn
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CHAPTER 4 USING URL ROUTINGwe requ
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C H A P T E R 9Writing Better JavaS
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• INDEXHTML5 local storage featur
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• INDEXURL routing, CheeseLux (co
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Pro JavaScript for Web AppsCopyrigh
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Contents• About the Author.......
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• CONTENTS• Chapter 3: Adding a
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• CONTENTSUsing Persistence in th
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• CONTENTSAdding Tests for a Modu
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About the Technical Reviewer RJ Owe
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