The Advantages and Disadvantages of JavaScript (Cont.)

Browser Programmability

While the language syntax and features of different versions of JavaScript are important, even more so is the browser being used to view your web pages. Let's go back to the basics to explain what this means in terms of JavaScript development.

JavaScript isn't able to do much without an environment, and in this book we're working with JavaScript in the browser. In this sense we could say that the browser is essentially the host. JavaScript's usefulness lies in its ability to manipulate the host environment, whether that's a web page, a PDF file, a web server, or Windows itself.

Each of these host environments makes itself available for programming. It does this by providing objects that allow JavaScript to learn about, and manipulate, the host environment. For example, the browser makes the document object that represents a web page available to JavaScript. This enables us to use JavaScript to add new HTML into a web page even as the user is viewing it. If we were using JavaScript in a Windows server then we'd find that the server exposes a very different set of objects with functionality related to the server.

So browsers themselves also have different levels of programmability: the collection of browser elements and features that can be accessed through a programming language. Just as the HTML supported by different browser versions varies, so too do the things we can access in the browser. A simple example would be the ability to change the image loaded in an IMG tag; this was supported by Netscape 3 but not by Internet Explorer 3, so attempting to access an IMG tag and change its source image will work great in one browser but fail completely in the other.

Not only do different browsers enable us to do different things in JavaScript, the way certain pieces of functionality are implemented can vary between browsers as well. For example, if we're creating pages accessible to IE4+ and NN4+ browsers, then we need to cope with three different ways of accessing HTML tags through JavaScript:

· The IE4+ way that works exclusively with IE4+

· The NN4 way that works exclusively with NN4

· The DOM Interface that works with IE5+ and NN6 browsers

We'll be covering each of these ways in depth in this book.

Coping with Different Browsers

You might be wondering how you can deal effectively with the panoply of JavaScript versions and web browsers' programmability. Well there's no denying that it can be frustrating, but there are strategies that you can adopt for dealing with browser issues that will make life that bit easier.

One option, and the one I prefer if possible, is to do two versions of a web site. The first version features maximum functionality and works on IE4+ and NN6. (As you'll see in later chapters, pages can be made to work with both IE4+ and NN6 with a little modification. Making IE4+ pages work with NN4 is much more of a challenge because of the limited programmability of NN4 compared with IE4, and the different ways that these browsers allow programmatic access.)

The second version is a more basic site, one that uses only simple HTML and limited JavaScript, if any at all, but which still allows access to most of the site's content. As long as I pay careful attention to the design of this second version of the site then I can expect it to work with 99% of browsers currently in use out there. Then when a visitor arrives at one of the pages in the web site I can use browser detection scripts, (which we'll be using later on), to redirect them to the version of our web site that works with their browser.

There will be times when this approach isn't going to work though. Sometimes the only way to make a web site function as well in NN4 as it does with IE4+ is to dumb down the original site specification. You'll also have to decide, on a site-by-site, audience-by-audience basis, whether you want to support older or less common modern browsers like Opera.

Three questions should help clarify which browsers your site needs to work with:

1. Who will visit the web site? If you're creating a web site dedicated to programming the Opera browser then it's going to have to work with Opera. Similarly, if you're developing for an Intranet where the browser and version is controlled then the question is answered for you.

2. What does the client want? If they demand it works with IE2.0 and remain oblivious to your raised eyebrows and sotto voce "you have got to be kidding", then that's what you're going to have to do.

3. Which browsers are most commonly used? This changes as new browsers are released and old ones go out of use.  You also need to take into account the importance of making your web site accessible – while this is obviously a good idea, there are also legal obligations to make certain web sites accessible.

There are a number of web sites that offer general statistics about the browser versions in common use, and these can help you decide which browser you need to support in order for the majority of people to view the site. Try these for web browser stats:

http://www.upsdell.com/BrowserNews/stat.htm

http://browserwatch.internet.com/stats/stats.html

http://www.w3schools.com/browsers/browsers_stats.asp

This last site covers information such as operating system, screen size and the version of JavaScript being used – including the fact that as many as 1 in 10 people have JavaScript switched off. (If you were building for such an audience then you might opt to have a non-JavaScript version of the web site, or create individual non-JavaScript pages, or notify users that they need JavaScript to use the web site. We'll be looking at ways of dealing with this as well as dealing with different screen sizes.)

Remember, though, that many browser statistic web sites base their numbers on the people who visit their web site, and the people who visit such sites are unlikely to be representative of the average visitor to your site. In fact, if you're creating web pages for an existing web site, then that web site is probably the best source of browser statistics.

The Advantages and Disadvantages of JavaScript
Practical JavaScript for the Usable Web
JavaScript in a Web Page