JavaScript Fundamentals
Hello, world!
This part of the tutorial is about core
JavaScript, the language itself. Later on, you’ll learn about Node.js and other
platforms that use it.
But we need a working environment to run
our scripts and, since this book is online, the browser is a good choice. We’ll
keep the amount of browser-specific commands (like
alert)
to a minimum so that you don’t spend time on them if you plan to concentrate on
another environment (like Node.js). We’ll focus on JavaScript in the browser in
the next part of
the tutorial.
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
<script> tag.
For instance:
|
<!DOCTYPE
HTML>
<html>
<body>
<p>Before the script...</p>
<script>
alert( 'Hello, world!' );
</script>
<p>...After the script.</p>
</body>
</html>
|
You can run the example by clicking the
“Play” button in the right-top corner of the box above.
The
<script> tag
contains JavaScript code which is automatically executed when the browser
processes the tag.
Modern markup
The
<script> tag has a few
attributes that are rarely used nowadays but can still be found in old code:
The
type attribute: <script type=…>
The old HTML standard, HTML4, required a
script to have a
type.
Usually it was type="text/javascript".
It’s not required anymore. Also, the modern HTML standard, HTML5, totally
changed the meaning of this attribute. Now, it can be used for JavaScript
modules. But that’s an advanced topic; we’ll talk about modules in another part
of the tutorial.
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