When a web cache has a requested resource in its store, it intercepts the request and returns its copy instead of re-downloading from the originating server.ĭata Cost is simply the idea that every operation, every function, every aspect of what we do with an API results in some sort of cost. application.Balancing Client And Server Caching in Web Application DevelopmentĬommunication APIs define rules of what interactions are possible between servers and communication applications.Ĭaching is a technique that stores a copy of a given resource and serves it back when requested. The next step is to enable the user to add items. Copy this line of code into the “Console,” and then refresh the page: leteDatabase('todos') Īfter refreshing, the “Resources” pane of “Developer Tools” should have changed and should now show the object store that we added: The “Resources” panel should now show the object store that was added. Otherwise, the structure of the data will be different from what your code expects, and you risk breaking the application.īecause this application doesn’t have any real users yet, we can fix this another way: by deleting the database. Whenever you add or remove object stores, you will need to increment the version number. The problem is that we haven’t incremented the version number, so the browser doesn’t know that it needs to run the upgrade callback. The code in onupgradeneeded never runs try adding a console.log in the onupgradeneeded callback to be sure. Having updated application.js, if you open the web app again, not a lot happens. This will create an object store keyed by timeStamp and named todo. styles.css body ) Ĭonsole.error('An IndexedDB error has occurred', e) ĭownload the contents of the minified IndexedDB polyfill, and put it in this file. Nothing surprising here: just a standard HTML web page, with an input field to add to-do items, and an empty unordered list that will be filled with those items. We will create the following files in a single directory: Scaffolding The Application And Opening A Database I’ll go through all of the steps using Google Chrome (and its developer tools), but there’s no reason why you couldn’t develop this application using any other modern browser.ġ. In my opinion, there is no reason to write any new code that integrates with WebSQL directly. Note: If you’re starting a new project and are deciding whether to use IndexedDB or WebSQL, I strongly advocate using IndexedDB and the polyfill. This will keep our code clean and easy to maintain, and once all browsers that we care about support IndexedDB natively, we can simply delete the polyfill. To support WebSQL, we’ll use an IndexedDB polyfill. Luckily, while we’ll need to use both, we’ll only need to think about IndexedDB. Veterans of the offline-first world might now be thinking, “But we could just use localStorage, which has the benefits of a much simpler API, and we wouldn’t need to worry about the complexity of using both IndexedDB and WebSQL.” While that is technically true, localStorage has number of problems, the most important of which is that the amount of storage space available with it is significantly less than IndexedDB and WebSQL. This is the deprecated predecessor to IndexedDB and the only option available on current versions of iOS (although iOS 8 will finally give us IndexedDB). This is the standard for client-side storage and the only option available on Firefox and Internet Explorer. In an ideal world, we’d use just one client database technology. The complete project is ready for forking on GitHub. run on the first- and second-most recent versions of all major desktop and mobile browsers.store all data locally, with no back end.allow the user to add and delete items in the to-do list.store data offline and load without an Internet connection.We’re going to make a simple offline-first to-do application with HTML5 technology. Matthew will also be running a “ Making It Work Offline workshop” at our upcoming Smashing Conference in Freiburg in mid-September 2014. In this article, Matthew Andrews, a lead developer behind FT Labs, shares a few insights he had learned along the way while building the FT application. Making an application work offline can be a daunting task.
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