One way that some poorly written scripts combine code to try to make the script work on additional browsers is to test a field called navigator.appName for various browser names. If you do a simple search of the code for the script and find a reference to this field name then chances are that the script probably contains code to do this and the script will most likely fail to work on at least some other web browsers. I recommend that you avoid scripts that reference this name within the script.
Another thing to search for is document.all. This was required for some scripts to work on Internet Explorer 4 (which just about no one uses any more). It also works witl some more recent browsers but not all of them. There is a different way that scripts should be coded in order that they will work with Internet Explorer 5+, Netscape 6+, Opera 5+, Mozilla, Firefox, Safari, Konquerer, and other modern web browsers. The easiest way to find out if the script is likely to support moderf web browsers other than Internet Explorer try changing all of the document.all references to document.ie4 and see if the code still works in your Internet Explorer 5+ browser. If it does then chances are reasonably good trhat the script will work in the other browsers as well. It may not but this is about as much of a test as you can do easily without having to install the other browsers to test the page there. Also there is no real need to change the code back, document.all only needs to be tested in order to get the script to work in Internet Explorer 4 and the chances are that no one will use such an old browser to visit your site. Of course if making this change stops the script from working then chances are that the script will NOT work in browsers other than Internet Explorer and you should search for a better script.
One final thing you can do to test if the script is likely to work in browsers other than Internet Explorer. If you go into the "Tools" Nemu and select "Internet Options" then go to the "Security" page and select the "Internet Zone" and "Custom Level" you will see some settings for ActiveX controls and plug-ins. You can set these five entries to "Prompt" or "Disable" and then salect "OK" to save the settings. If you now view your page and try to run the script it will run if it doesn't use ActiveX and it will fail to run or will prompt you to approve it before it runs if it does use ActiveX. ActiveX is also only available on Internet Explorer and so the script that fails this test is guaranteed not to work on other browsers and should be avoided.
I can't guarantee that a script that passes these three tests will work properly on all of the different browsers that people use. The only way to guarantee that is to actually test the script in all of those browsers. What I can guarantee is that any script that fails any of these simple tests is not going to run properly on all of the different browsers that your visitors will be using and that the person who wrote the script did not adequately test the script before making it available for you to copy.
If you perform these tests on any pre-built script that you are thinking of using on your site and make sure that the script passes these tests then there is a reasonable chance that the script will run on at least most of the more popular web browsers. If you only use scripts that pass these tests then you will have a more visitor friendly web site than you might have had if you had not performed the tests and you still haven't had to go to all the trouble of learning Javascript for yourself.
