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CHAPTER 10 ■ SCRIPTING BOM 400 New Balance Nike Saucony Note that the three sprites now have four arrows (as displayed in Figure 10–1). We’ll need those to scroll the galleries. Figure 10–1. The blue, fuchsia, and green sprites now have four arrows.
Remembering Visitor Data with Cookies CHAPTER 10 ■ SCRIPTING BOM In Chapter 9, we wrote a skin-swapping behavior. However, if you click Refresh in Firefox to reload ten.html, JavaScript totally forgets which skin you preferred. Similarly, if you close Firefox, the next time you open ten.html, the skin reverts to blue, which is the default. So, we need to find a way to give JavaScript a memory. For this, BOM provides cookies. Our goal will be to save a visitor’s skin preference to a cookie. That way, we can preset the skin to their favorite skin. We ought to make them feel welcome. However, working with cookies is not entirely straightforward. On the one hand, writing a cookie is simple. Just assign name value pairs, separated by semicolons, to document.cookie, and you’re done. Here are a couple of name-value pairs: name=john;preference=blue On the other hand, reading a cookie is a nightmare. JavaScript returns the name-value pair of every cookie, joined by semicolons, in one long string. It’s sort of like the ticker tapes that stock exchanges used to work with. You have to search through all those cookies for the one you want. That’s ridiculous, of course. But with BOM, ridiculous is the status quo. With this in mind, it makes sense to write a helper function to read the value of a cookie. There’s no need to write a second one to write the value of a cookie, since that is simple enough. Getting the User’s Preference Open ten.js, which right now is just the final code for nine.js, in your preferred text editor. Scroll down to just past doZ(), the last helper function we coded in Chapter 9, and insert a new helper function named getCookie(). Then define a name parameter, which will contain the name of the cookie to clip from the ticker-tape string in document.cookie: function getCookie(name) { } Now define some local variables: • batch will contain the ticker-tape string in document.cookie. • i will contain the return value of passing name concatenated to = to String.indexOf(). Remember from Chapter 2 that this wrapper method returns the offset from the beginning of the string or -1 to convey failure. i will enable us to clip our cookie from batch. • Just let firstCut and secondCut default to undefined for now. Thus far we have this: function getCookie(name) { var batch = document.cookie, i, firstCut, secondCut; i = batch.indexOf(name + "="); } So if JavaScript can find our cookie in batch, i will not contain -1. Let’s write an if conditional for i !=== -1 before we go any further: function getCookie(name) { var batch = document.cookie, i, firstCut, secondCut; i = batch.indexOf(name + "="); 401
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THE EXPERT’S VOICE ® IN WEB DEVE
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ii JavaScript for Absolute Beginner
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iv Contents at a Glance ■Contents
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■ CONTENTS vi ■Chapter 2: Type
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■ CONTENTS viii Sharing a Prototy
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■ CONTENTS x Querying Attributes
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■ CONTENTS xii Getting the User
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■ CONTENTS xiv About the Technica
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■ PREFACE xvi Preface In the 2005
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■ PREFACE xviii Opening Firebug L
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■ PREFACE xx Now press Return on
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■ PREFACE xxii editor reappear. N
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■ PREFACE xxiv
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CHAPTER 1 ■ REPRESENTING DATA WIT
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CHAPTER 2 ■ TYPE CONVERSION 26 Fi
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CHAPTER 2 ■ TYPE CONVERSION 30 St
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CHAPTER 2 ■ TYPE CONVERSION 32 De
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CHAPTER 2 ■ TYPE CONVERSION 50 Co
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CHAPTER 2 ■ TYPE CONVERSION 54 To
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CHAPTER 3 ■ OPERATORS 58 Remember
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CHAPTER 3 ■ OPERATORS 60 Using Ja
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CHAPTER 3 ■ OPERATORS 62 dough.po
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CHAPTER 3 ■ OPERATORS 64 mincedLe
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CHAPTER 3 ■ OPERATORS 66 Figure 3
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CHAPTER 3 ■ OPERATORS 68 // 1.25
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CHAPTER 3 ■ OPERATORS 70 • If b
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CHAPTER 3 ■ OPERATORS 72 The impo
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CHAPTER 3 ■ OPERATORS 76 } }; pur
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CHAPTER 3 ■ OPERATORS 78 saigonCi
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CHAPTER 3 ■ OPERATORS 82 loganber
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CHAPTER 3 ■ OPERATORS 92 tartar:
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CHAPTER 3 ■ OPERATORS 94 fridge.y
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CHAPTER 3 ■ OPERATORS 96
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CHAPTER 4 ■ CONTROLLING FLOW 98 s
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CHAPTER 4 ■ CONTROLLING FLOW 100
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CHAPTER 5 ■ MEMBER INHERITANCE 14
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CHAPTER 6 ■ FUNCTIONS AND ARRAYS
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CHAPTER 7 ■ TRAVERSING AND MODIFY
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CHAPTER 8 ■ SCRIPTING CSS 308 Rem
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CHAPTER 8 ■ SCRIPTING CSS 310 var
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CHAPTER 8 ■ SCRIPTING CSS 312 tex
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CHAPTER 8 ■ SCRIPTING CSS 314 Fig
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CHAPTER 8 ■ SCRIPTING CSS 326 One
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CHAPTER 8 ■ SCRIPTING CSS 336 Why
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CHAPTER 8 ■ SCRIPTING CSS 340 Ref
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CHAPTER 9 ■ LISTENING FOR EVENTS
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■ INDEX 462 parsing an XML respon
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■ INDEX 464 creating, 217 queryin
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■ INDEX 466 document.styleSheets,
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■ INDEX 468 listening for mousedo
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■ INDEX 470 chaining prototypes,
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■ INDEX 472 definition of, 255 de
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■ INDEX 474 ■ P padJSON(), 445
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■ INDEX 476 ten.js, 401 ternary o
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