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CHAPTER 7 CREATING RESPONSIVE WEB APPS};Modernizr.load([{test: window.matchMedia,nope: 'matchMedia.js',complete: function() {var screenQuery = window.matchMedia('screen AND (max-width:500px)');deviceConfig.smallScreen = ko.observable(screenQuery.matches);if (screenQuery.addListener) {screenQuery.addListener(function(mq) {deviceConfig.smallScreen(mq.matches);});}deviceConfig.largeScreen = ko.computed(function() {return !deviceConfig.smallScreen();});}}, {test: Modernizr.touch,yep: 'jquery.touchSwipe-1.2.5.js',callback: function() {$('html').swipe({swipeLeft: advanceCategory,swipeRight: advanceCategory});}},{complete: function() {callback(deviceConfig);}}]);When you pass an array of objects to the Modernizr.load method, each test is performed in turn. Ihave added a test that uses the Modernizr.touch check and that loads the touchSwipe library if touchsupport is present.• Tip Make sure you included the touch tests if you downloaded your own version of Modernizr. The version Iincluded in the source code for this chapter contains all of the available tests.Notice that I used the callback property to set up support for handling swipes. Functions set usingthe callback property are executed when the specified resources are loaded, whereas functions specifiedusing complete are executed at the end of the test, irrespective of the test result. I want to handle swipeevents only if touchSwipe has been loaded (which itself indicates that touch support is present), so Ihave used callback to give Modernizr my function.The touchSwipe library is applied using the swipe method. In this example, I have selected the htmlelement as the target for detecting swipe gestures. Some browsers limit the body element size so that itdoesn’t fill the entire window when the content is smaller than the available space. This isn’t usually a190www.it-ebooks.info
CHAPTER 7 CREATING RESPONSIVE WEB APPSproblem, but it creates dead spots on the screen when dealing with gestures, which may not be targetedat individual elements. The simplest way to get around this is to work on the html element.The touchSwipe library is able to differentiate between different kinds of touch events and swipes ina range of directions. I care about swipes only to the left and the right in this example, which is why Ihave defined a function for the swipeLeft and swipeRight properties in the object I passed to the swipemethod. In both cases I have specified the advanceCategory function, which is the same function I usedto change selected categories earlier. The result is that swiping left moves to the previous category andswiping right goes to the next category. The last point to note about this listing is the last item in thearray passed to the Modernizr.load method:{}complete: function() {callback(deviceConfig);}I don’t want to invoke the callback function until I have set up all of the device details in the resultobject that will be added to the view model. The easiest way to ensure this happens is to create anadditional test that contains just a complete function. Modernizr won’t execute this function until all ofthe other tests have been performed, the required resources have been loaded, and the callback andcomplete functions for all of the previous tests have been performed.Using Touch to Navigate the Web App HistoryIn the previous example, I respond to swipe gestures by looping through the available productcategories. In this section, I show you how to respond to these gestures in a more useful way.The temptation is to use the browser’s history to respond to swipes. The problem is that there is noway to peek at the previous or next entry in the history and see whether it is one that belongs to the webapp. If it isn’t, then you end up making the user navigate away from your web app, potentially to a URLthat they had no intention of visiting. Listing 7-15 shows the changes required to the enhanceViewModelfunction in the utils.js file to set up the basic support for tracking the user’s category selections.• Tip You could elect to use local storage and make the swipe-related history persistent. I prefer not to do this,since I think it makes more sense for the history to be limited to the current life of the web app.Listing 7-15. Adding Application-Specific History Using Session Storagefunction enhanceViewModel() {cheeseModel.selectedCategory = ko.observable(cheeseModel.products[0].category);mapProducts(function(item) {item.quantity = ko.observable(0);item.subtotal = ko.computed(function() {return this.quantity() * this.price;}, item);}, cheeseModel.products, "items");191www.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 2 GETTING STARTED($0)Total
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CHAPTER 2 GETTING STARTEDSummaryAs
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CHAPTER 3 ADDING A VIEW MODELCreat
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CHAPTER 3 ADDING A VIEW MODEL$('#b
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C H A P T E R 4Using URL RoutingIn
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C H A P T E R 5Creating Offline Web
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CHAPTER 5 CREATING OFFLINE WEB APP
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C H A P T E R 6Storing Data in the
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Page 229 and 230: 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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