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What is going on here? We’ve used the onMouseOver event handler to tell the browser that some- thing is supposed to happen when the visitor’s mouse hovers over this link. The event handler is followed by the equal sign in the same way that links and other standard bits of HTML use the equal sign. As you may have guessed, window.status is JavaScript’s charming way of referring to the status bar at the bottom of the web page. (The status bar is the part of the browser that usually displays the bare-naked URL, gen- erally at the lower left.) Without getting too hairy, JavaScript gives each object in its document model an address based on the object’s position within the document’s hierarchy, moving from the top level of the hierar- chy down to the details: window is a top-level object; status is the object being modified via JavaScript. (Like we said, buy the JavaScript books if you want a better explanation, and you probably do.) Notice that the status bar message text ‘FASHION MAVEN fashions for men.’ is enclosed within single quotation marks. This is because the JavaScript itself is enclosed within double quotation marks. If the text also used double quotation marks, the browser would not know how to distin- guish the quoted JavaScript from the quoted text. Observe also that both the description and the phrase return true end in a semicolon. This is basic JavaScript syntax, so get used to it. There are more semicolons in JavaScript than in all Charles Dickens’s novels combined. Technically, the semicolon is not required when a JavaScript statement ends the line. So, window.status = “some thing” is perfectly valid JavaScript in the context of a function, a la: <script type=”text/javascript”> function rollover() { window.status = “some thing” // no semicolon } </script> But if you are placing two or more statements on a single line, as you would inside an event handler attribute, you must separate the statements by semicolons. 296 HOW: The Joy of JavaScript: The Dreaded Text Rollover 15 0732 CH11 4/24/01 11:23 AM Page 296 Finally, note that return true is used at the end to handle the event. It tells the browser to follow the HTML link. Return false would tell the browser not to follow the link, which can be useful when you don’t want to load a new page. Status Quo So far, so good—now let’s make our little example even more exciting. (Well, as exciting as this kind of stuff gets.) Let’s craft a message that shows up in the status bar when the visitor stops hovering over the link: Explore FASHION MAVEN <a href=”/fashions/men/” onMouseOver =”window.status= ➥’FASHION MAVEN fashions for men.’; return true;” onMouseOut=”window ➥status=’Welcome to FASHION MAVEN.’; return true;”>fashions for men</a>. What have we done? (Besides further prostituting ourselves to FASHION MAVEN, that is.) We’ve used exactly the same syntax to replace the onMouseOver message with a default status bar message. When the user places the mouse pointer over the link, he’ll read “FASHION MAVEN fashions for men.” When he releases the mouse, our insistent client will replace that link-specific brand message with a general one: “Welcome to FASHION MAVEN.” This general message will remain in the visitor’s status bar until he moves the mouse over a new link. If we had not done this, “FASHION MAVEN fashions for men” would have been “stuck” in the status bar window even after the vis- itor removed his mouse from that link. None of what we’ve just shown you requires any custom scripting or prepa- ration in the <HEAD> of the HTML document. The onMouseOver and onMouseOut event handlers are as old as the hills, and any JavaScript- capable browser will handle this code natively. (As we’ll see later, other JavaScript techniques require a script before the function itself.) Well, this is fine for a single link, but coding identical onMouseOut mes- sages for a dozen links seems like a lot of work, doesn’t it? There ought to be a shortcut! And fortunately, there is. (Programmers are always creating shortcuts.) 297 Taking Your Talent to the Web 15 0732 CH11 4/24/01 11:23 AM Page 297 In the <BODY> tag of our HTML document, we can add this line of code: <body onLoad=”window.defaultStatus=’Welcome to FASHION MAVEN.’”> For the sake of simplicity, we’ve left out the rest of the markup you might normally include in the <BODY> tag, such as the default background color, text color, and so on. Of course, if you’re following W3C recommendations and using CSS to handle your site’s stylistic elements, then your <BODY> tag can be as simple as <BODY> with no extra junk inside it. As you have probably deduced, onLoad is another event handler. In this case, the event is the loading of the web page itself. When the page loads (the event), a function must be performed. In this case, you’ve instructed the browser that the required function is a change in the status bar mes- sage. Thanks to your cleverness, even before the visitor hovers over a link, the status bar at the bottom of the browser will proudly proclaim, “Wel- come to FASHION MAVEN.” Can you feel your client’s love? We can. You have now carried your client’s brand down to the level of the status bar. Had you not done this, the status bar would read “Internet Zone” or some- thing equally meaningless (as far as your client is concerned). But wait, there’s more! Because the onLoad event handler in our <BODY> tag is telling the browser to proclaim “Welcome to FASHION MAVEN.” by default, we can simplify our JavaScript link as follows: Explore FASHION MAVEN <a href=”/fashions/men/” onMouseOver =”window.status= ➥’FASHION MAVEN fashions for men.’; return true;” onMouseOut=”window status=’’; ➥return true;”>fashions for men</a>. What changed? Look closely. We’ve removed the redundant text “Welcome to FASHION MAVEN” and replaced it with Folger’s Crystals. Just kidding. Actually, we’ve replaced it with an empty pair of single quotations, which tell the browser to revert to the default text specified by the onLoad event handler (“Welcome to FASHION MAVEN”), We no longer have to type “Wel- come to FASHION MAVEN.” in the JavaScript text link itself. That may not seem like much of an achievement. That’s because it’s not much of an achievement. But if there are a dozen links on this page, all requiring JavaScript text messages, we’ve saved ourselves the trouble of typing the same onMouseOut text 12 times. We’ve also saved the viewer the trouble of downloading those few kilobytes of redundant text. 298 HOW: The Joy of JavaScript: The Dreaded Text Rollover 15 0732 CH11 4/24/01 11:23 AM Page 298 Notice that it is possible to create dynamic web effects in web pages that live on your desktop—without requiring a web server. Hooray for JavaScript! A Cautionary Note Like everything you can do on the Web, modifying the default status bar message involves trade-offs and thus requires thought. Browsers use defaultStatus to communicate with users, letting them know if they’ve connected or not, informing them when an object is being downloaded, and letting the geeks in the house keep track of the actual URLs to which your links point. Modifying defaultStatus can enhance site branding and please your client, but it might upset some users, so don’t use JavaScript in this way unless the benefits outweigh the drawbacks. Kids, Try This at Home Before we go any further, try reproducing the JavaScript effects we just described in a simple HTML page you’ve written. Needless to say, you will not win any innovation awards, but it might help you conquer any linger- ing fear of programming. If you can do this simple thing, you can do other, somewhat more complex things. When it works on a page you’ve created, you’ll begin to feel like a web designer. If it doesn’t work, you’ll really begin to feel like a web designer. Then you’ll go back and fix your syntax. Speaking of which… The fine print Because single quotation marks are used to denote the beginning and end- ing of text messages, what do you do if your text includes an apostrophe? After all, in HTML, an apostrophe is exactly the same as a single quotation mark. What you do is “escape” the single quotation mark by inserting a backslash character in front of it. Lip smackin’ good! Get <a href=”/recipes/stupidcomeon.html “ onMouseOver ➥=”window.status=’Our chef\’s favorites.’; return true;” onMouseOut=”window status=’’; ➥return true;”>the recipes</a>. 299 Taking Your Talent to the Web 15 0732 CH11 4/24/01 11:23 AM Page 299 Notice that we don’t refer to our chef’s favorites; we refer to our chef\’s favorites. The backslash character tells the browser to treat the quotation mark as a quotation mark, not a string terminator (meaning, not the end of a JavaScript statement). Forgotten backslashes have caused many a web designer her share of sleepless nights. Return of the son of fine print Yep, one more tip. Forget the semicolon, and you will create JavaScript errors in many browsers, which unfortunately will not show up in many others. That’s unfortunate because if you can’t see the error, you might not realize it’s in there—so you may not know to fix it. For some reason, Macs seem especially forgiving of the missing semicolon error. Many a Mac-based web designer has uploaded a web page (or an entire site) and gone off to smoke reefer, little realizing that he has left a trail of JavaScript syntax errors behind him. The moral, of course, is to check your JavaScript syntax carefully, test on multiple platforms, and avoid smoking reefer—especially that overpriced brown stuff they’re sell- ing uptown. The Not-So-Fine Print It’s worth pointing out again that some web users, including hardcore geeks, detest this flippant toying with the sanctity of the status bar. These users want to know which URL your link will take them to. They deeply resent your hiding this information from them with stupid text about FASHION MAVEN. Some might even avoid clicking the link out of paranoid fear. (“Dude, if I can’t see the link, I don’t know where you’re taking me.”) Thus they will never learn about FASHION MAVEN’s extensive selection of plaids and corduroys for tall men, short men, fat men, and cadets, all at prices 10% below what department stores usually charge. You think we are making this up, but you haven’t read our email and haven’t spent years watching flame wars erupt on web design mailing lists. You think people will click links without worrying about or even noticing these changes in the expected status bar message. Many people, of course, won’t notice; many others will notice and not care; some will notice and be pleased. But others will be displeased, and a few may even write letters of complaint. 300 HOW: The Joy of JavaScript: The Dreaded Text Rollover 15 0732 CH11 4/24/01 11:23 AM Page 300 These people are out there, and some of them might be among your clients’ favorite customers. Thus, your infinitesimal gain in branding could be off- set by a commensurate loss of audience. Even this small a decision is worth considering carefully. It’s also worth mentioning that, with the rise of HTML’s <TITLE> attribute: <a href=”somelink.html” title=”Information about this link.”> …there is now an easier way to enhance the information conveyed by a link. In IE4 (and higher), Netscape 6 (and higher), Opera 5, iCab, and Mozilla, the <TITLE> attribute will cause a Windows-like Tool Tip or Mac OS Help bal- loon to pop up when the user hovers over the link. (In Opera, the message appears in the browser’s status bar, just like a JavaScript mouse-over text.) This Tool Tip or Help balloon will contain the text you’ve written inside the quotation marks following the word title and the equal sign. To avoid over- whelming users with flying tool tips, there is usually a slight delay before the Tool Tip appears. There is also no need to worry about escaped charac- ters when writing <TITLE> attribute text: <a href=”somelink.html” title=”It’s exciting not to worry about apostrophes, isn’t it? Gosh, ➥it’s really swell.” Of course, if your <TITLE> text includes a double quote, the browser could get confused: <a href=”/” title=”We say “no!” to drugs.”> Instead, use single quotations: <a href=”/” title=”We say ‘no!’ to drugs.”> Not only is this <TITLE> attribute method marginally easier to use than JavaScript, it is also, in some ways, more logical. When a user has her eye on a link (or a linked image), her eye does not wish to jump down to the browser status bar. Her eye wants to say where it is. In IE4+ and Netscape 6, the <TITLE> attribute accommodates this natural behavior of the human eye and mind because the Tool Tip or Help balloon pops up adjacent to the link itself. Still, we do not wish to discourage you from using status bar messages. 301 Taking Your Talent to the Web 15 0732 CH11 4/24/01 11:23 AM Page 301 They make a handy informational and branding tool, and they work in older browsers (like Netscape 4) that don’t support the <TITLE> attribute. THE EVER-POPULAR IMAGE ROLLOVER Problem: The site is pretty but feels lifeless. Visitors are encouraged to admire but not to click and explore. The site needs a shot of GUI-like, visual interactivity. Solution: The JavaScript image rollover (see Figures 11.2 and 11.3). 302 HOW: The Joy of JavaScript: The Ever-Popular Image Rollover Figure 11.2 Kaliber 10000, “The Designer’s Lunchbox,” is a jewel of graphic and navi- gational design with numerous JavaScript tricks up its virtual sleeve. Note the “K10k back issues” pull-down menu at the upper right, the code for which is described later in this chapter. One of K10k’s simpler (but very effec- tive) techniques is using the ever-popular image rollover to replace static icons with animated ones. For instance… Figure 11.3 …dragging your mouse cursor over the Rants and Raves button replaces the static dog with a GIF ani- mation of a pooping dog. Hey, we said they were brilliant web designers; we didn’t say they were mature (www.k10k.net). 15 0732 CH11 4/24/01 11:23 AM Page 302 Let’s assume that after reading Chapter 9, “Visual Tools,” you opened Pho- toshop and ImageReady, designed a web page comp, sliced it, and used ImageReady to generate the JavaScript rollover. Now take those same sliced images, open your HTML text editor of choice (Allaire Homesite, Barebones BBEdit, or Optima-Systems PageSpinner), and, using the tech- niques you learned in the books or online tutorials mentioned earlier in this chapter, write yourself an image rollover by hand. You can do it! It’s okay to prop the books open in front of you or to refer back to Thau’s web pages. You’ll create links much like the text links we showed in the previous example. You’ll also hand-code a preload, usually in the <HEAD> of your document. A preload ensures that swapped images will be downloaded to the user’s cache before the page displays. In that way, those preloaded images are ready to leap into action the moment the user drags her mouse over them. Why are rollover effects so popular? We think it is because users are accus- tomed to operating systems whose GUIs respond to their actions. Rollovers emulate this behavior, and they indicate that an image is more than an image—it is a dynamic trigger to an action the user can perform. Users dig that stuff. A Rollover Script from Project Cool On the assumption that you haven’t bought those other books yet, haven’t read any of the online tutorials, and still feel uncomfortable with JavaScript, we’ll go ahead and show you another simple way to create JavaScript image rollovers. The following was adapted from a basic script at Project Cool. And that’s okay. Project Cool wrote their script back in the late 1990s so web design- ers would use it and learn from it. The future of Project Cool is doubtful because the site’s creators left in late 1999, but this script and others like it were still available online as of this writing (www.projectcool.com). <script type=”text/javascript”> <! Adapted from Projectcool.com if (document.images){ 303 Taking Your Talent to the Web 15 0732 CH11 4/24/01 11:23 AM Page 303 mainover = new Image; mainout = new Image; mainover.src = “/images/menubar_over_1.gif”; mainout.src = “/images/menubar_out_1.gif”; storiesover = new Image; storiesout = new Image; storiesover.src = “/images/menubar_over_2.gif”; storiesout.src = “/images/menubar_out_2.gif”; } functiover swapem(iname, gname) { if(document.images){ iname.src = gname.src; } } // > </script> This script goes inside the <head></head> of an HTML document. It might look complex if you’re unfamiliar with JavaScript, but it is really elegantly simple. The script begins by announcing the fact that it is a script and that its type is text/javascript. Older browsers expected to see a <LANGUAGE> attrib- ute with the name and, optionally, a version of the scripting language being used (“Javascript1.2,” for instance), but this attribute has been deprecated in favor of a more generic <MIME> type descriptor. Don’t worry if you don’t understand what we just said; simply relax and type: <script type=”text/javascript”> Similarly, the end of the script is announced by a </script> tag. As with HTML and CSS, <comment> tags tell search engine spiders (and non- JavaScript-capable browsers) to ignore everything written between <! and >. You want search engines to help web users find your content, not your JavaScript. Next, the Project Cool script sets a condition for running. Early versions of JavaScript did not support image rollovers. The script wants to make sure it is working with a browser that understands rollovers, so it tests the browser’s receptivity to the images array object of the document model: if (document.images) 304 HOW: The Joy of JavaScript: The Ever-Popular Image Rollover 15 0732 CH11 4/24/01 11:23 AM Page 304 The script could have accomplished the same thing by detecting for browsers and platforms (a technique known as browser sniffing). For instance, it could have checked for the presence of Netscape 2 and Inter- net Explorer 3, two browsers that did not support the images array of the document model (and hence would not be able to process this script). But the code to check for these browsers is somewhat long compared to a sim- ple line such as if (document.images) Besides, some versions of IE3 did understand image rollovers. Rather than get tangled in browser versions, it is easier, more elegant, and more reli- able to test for an understanding of the document images object. If the browser does not understand (document.images), the script will be skipped. If the required conditions are met, the script runs. The script next declares two image conditions (Over or Out) and preloads the required images (mb3_on-01-01.gif, mb3_off-01-01.gif, mb3_on-02- 01.gif, and mb3_off-02-01.gif): if (document.images){ mainover = new Image; mainout = new Image; mainover.src = “/images/menubar_over_1.gif”; mainout.src = “/images/menubar_out_1.gif”; storiesover = new Image; storiesout = new Image; storiesover.src = “/images/menubar_over_2.gif”; storiesout.src = “/images/menubar_out_2.gif”; Over corresponds to the onMouseOver state, and off corresponds to the default and onMouseOut state. The two images correspond to two named JavaScript objects (main and stories). Finally, the script declares a swapem function, which works by swapping one image state for another: function swapem(iname, gname) { if(document.images){ iname.src = gname.src; 305 Taking Your Talent to the Web 15 0732 CH11 4/24/01 11:23 AM Page 305 [...]... name (main), allowing the swapem function to recognize the image as the object that is supposed to be swapped The remaining , , , and attributes should be familiar to you from the HTML chapter The and attributes are included so that the menu item will 15 0732 CH11 4/24/01 11:23 AM Page 307 Taking Your Talent to the Web remain accessible to those who surf with... in The Wizard of Baghdad The point is that JavaScript allows the user to select exactly the level of detail needed (www.tvguide.com) Get Your Together Before you can create a new window, you must define it in the HTML of your HTML document Here is a typical way to do just that: Welcome to Porkchops.com! 15 0732 CH11 4/24/01 11:23 AM Page 309 Taking Your Talent. .. nongraphical browsers such as Lynx The link to /main.html will work even if JavaScript has been turned off in the user preferences (or the browser does not support JavaScript) The code and the effect on the web page are much simpler than the descriptive text you’ve just waded through You might ask, can JavaScript text rollovers be added to an image rollover like the one just described? The answer is yes, and it... because this is the “MouseOver” state for the image object The onMouseOut event handler also declares two variables for the swapem function: a named object (main) and an appropriate image state (mainout)—out, because this is the “MouseOut” state for the image object Semicolons follow the naming of the variables and the required return true declaration The image tag that follows gives the source image... When the event is triggered by the user’s action (clicking the link), the named window.open function will be performed, and the appropriate HTML page will appear in a 350 x 400 pop-up window with no status bar or menu bar The return false will prevent the browser from following the URL specified in the , for backward compatibility As a courtesy, it’s nice to include a function in the. .. window.status=’Visit the ➥main page.’; return true;” onMouseOut=”swapem(main, mainout); window.status=’’; ➥return true;”> WINDOWS ON THE WORLD Problem: The site offers streaming video files You, the client, or the information architect want these files to play back inside the. .. want these files to play back inside the browser via the QuickTime plug-in (see Chapter 12) It is easy to use the HTML or tags to embed a QuickTime movie in a thoughtfully designed HTML page But if you do this on the current page, the movie will begin streaming even if visitors do not have the bandwidth or patience to see it Solution: The JavaScript pop-up window Opening new windows via... familiar to you because it is fairly similar to the dreaded text rollover Once again, here is a standard HTML link followed by two event handlers: one for onMouseOver, the other for onMouseOut But now, instead of invoking a status bar message, our MouseOver and MouseOut states call upon the swapem function declared earlier in the document The onMouseOver event handler declares two variables for the swapem... happen in their existing browser window These folks hate pop-up windows, remote controls, and everything else that can happen outside the safe, familiar world of their existing browser window Are these users right? They are right for themselves What does this mean? It means that pop-up windows, remotes, and other such stunts should never be created lightly or purposelessly (Why offend visitors if you... And in the pop-up window we can use the dapper and elegant closeme.gif: )”> And that’s all there is to it AVOIDING THE HEARTBREAK OF LINKITIS Problem: The client insists on a menu with dozens of choices You know such a menu will be ugly and confusing and will cause visitors to scroll . change in the status bar mes- sage. Thanks to your cleverness, even before the visitor hovers over a link, the status bar at the bottom of the browser will proudly proclaim, “Wel- come to FASHION. mind because the Tool Tip or Help balloon pops up adjacent to the link itself. Still, we do not wish to discourage you from using status bar messages. 301 Taking Your Talent to the Web 15 0732. used the onMouseOver event handler to tell the browser that some- thing is supposed to happen when the visitor’s mouse hovers over this link. The event handler is followed by the equal sign in the
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