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Web Design in a Nutshell, 2nd Edition by Jennifer Niederst Robbins

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Handling Multiple Browsers

Unlike CGI scripts, which run on the server and don’t require any particular intelligence on the part of the browser, JavaScript code is completely dependent on browser support. If you put a script on your page, browsers that don’t understand JavaScript won’t know what to do with it. As I mentioned earlier, these browsers will interpret the code as straight text, and the result is rather unpleasant.

It’s even more unpleasant, however, when your code isn’t completely understood by a JavaScript-aware browser. As we’ve already discussed, different browsers, and different versions of the same browser, support different versions of JavaScript. A poorly written script can generate error messages or even crash a user’s browser, which discourages return visits. Fortunately, JavaScript provides ways to target the browsers that understand specific JavaScript elements.

Checking for Browsers

If you have a script that you know works in Netscape 6 and IE 5.5 but doesn’t work in older browsers, you may want to check browser versions and serve your script to users of the browsers in which it works, but not to users of older browsers. Using the techniques shown in this section, you can serve different scripts to different browsers. This means you can write different scripts for people using the latest browser versions and for users of the Version 4.0 browsers, for example. And you can also have an HTML-only option for browsers that don’t support JavaScript (or have it ...

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