INLINE CODE VERSUS EXTERNAL FILES

Although it's possible to embed JavaScript in HTML files directly, it's generally considered a best practice to include as much JavaScript as possible using external files. Keeping in mind that there are no hard and fast rules regarding this practice, the arguments for using external files are as follows:

• Maintainability—JavaScript code that is sprinkled throughout various HTML pages turns code maintenance into a problem. It is much easier to have a directory for all JavaScript files so that developers can edit JavaScript code independent of the markup in which it's used.
• Caching—Browsers cache all externally linked JavaScript files according to specific settings, meaning that if two pages are using the same file, the file is downloaded only once. This ultimately means faster page-load times.
• Future-proof—By including JavaScript using external files, there's no need to use the XHTML or comment hacks mentioned previously...