Wikipedia provides a more detailed introduction to this web programming language.
This is the code to include an external script file. In this case the file is named site.js. The main advantage of using an external file is that the code can be shared by many Web pages allowing much easier modifications in the future.
We have already looked, briefly, at comments in the code sample above. The comment in that sample is a multiple line comment indicator. A single line indicator is simply //.
// This is a single line comment
/* And this is a longer section of comment
that will span multiple lines */
It is good practice to include comments in all code that you develop, even if it is only you that will be using the code. It is surprising how quickly you forget what the code was intended to do, when you revisit it several weeks or months later.
Comments are even more important if the code is likely to be viewed by other program developers. As they will not, necessarily, know your objectives from the code itself.
This introduction is, as the name implies, simply an introduction to the topic. At the time, it looked to be the language of the future. But, the world of computing evolves with frightening speed and other languages soon appeared on the scene.