If you look at other people’s web pages, you’ll notice that sometimes they’ll put JavaScript right inside their web pages, instead of putting it into a separate file as we’ve done here. I recommend against this. By putting your JavaScript into a separate JavaScript (.js) file, you can call the same file from different web pages. If a new browser version necessitates changing your JavaScript code to overcome a new bug, you’ll be able to make the change once, instead of looking for all the web pages you’ve used something like that code in. You’ll always miss at least one.
Separating your JavaScript into its own file also makes it much harder for your JavaScript to interfere with your HTML in browsers that don’t implement JavaScript, or don’t implement it the way you expect it to work.
You can put more than one <script src="…"> in your web pages, to reference more than one set of JavaScripts. Just make sure your JavaScript functions all have unique names.
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