JavaScript - Introduction

This part of the tutorial is about core JavaScript, the language itself.

So first, let’s see how we attach a script to a webpage. For server-side environments (like Node.js), you can execute the script with a command like "node my.js".

The “script” tag

JavaScript programs can be inserted into any part of an HTML document with the help of the 

...After the script.

You can run the example by clicking the “Play” button in the right-top corner of the box above.

The 

This trick isn’t used in modern JavaScript. These comments hide JavaScript code from old browsers that didn’t know how to process the 

Here, /path/to/script.js is an absolute path to the script from the site root. One can also provide a relative path from the current page. For instance, src="script.js" would mean a file "script.js" in the current folder.

We can give a full URL as well. For instance:

To attach several scripts, use multiple tags:

…

Please note:

As a rule, only the simplest scripts are put into HTML. More complex ones reside in separate files.

The benefit of a separate file is that the browser will download it and store it in its cache.

Other pages that reference the same script will take it from the cache instead of downloading it, so the file is actually downloaded only once.

That reduces traffic and makes pages faster.

If src is set, the script content is ignored.

A single 

We must choose either an external 

Summary

• We can use a .