Introduction to JavaScript
These notes are not aimed at professional programmers. I'm assuming that you've written
some web sites and now need to add a little bit of interaction. You're not working in a
large team and a site that works is more important than a site which meets all the latest
software engineering standards. I'm going to start off by cutting corners and simplifying
things as far as I can. My aim is to get you to the point where you can write a program
that works. Then I'll give some links to sites that will take you further.
Think of it as learning to drive. When you begin to learn you are really happy if you can
start and stop the car and drive across an empty car park without hitting anything.
Understeer, oversteer and double declutching (ask your father) can come later.
As with learning to drive, you can't learn JavaScript by reading about it. You have to do
it and that means writing your own programs. Please try all the examples and explore
what will happen if you make changes to the programs. You can't hurt anything and you've
got to experiment. None of your experiments will fail. Your modified programs might not
run but if you can find out why they don't run then in terms of learning, that's a
success.
HTML
I'm assuming that you can write a simple web page using HTML. If you are happy with this
level of complexity:
<html>
<head>
<title>
My first web page
</title>
</head>
<body>
This text will appear on the page.
</body>
</html>
then you know enough HTML to be able to work through my pages here.
If the snippet of HTML quoted above is a mystery to you then I suspect you've been using
some program where you design the layout of your page and it then generates the HTML
automatically. I'm afraid you'll need to get closer to the code in order to be able to
write JavaScript programs. It's not something that can be automated.
Actually, it can be automated but you can only then produce what the automatic program
generator has been programmed to produce. You'll be very restricted.
What is JavaScript?
JavaScript is a scripting language which means that it cannot be used to write a stand-
alone program. A JavaScript program can't run without some sort of assistance and you'll
be running your programs inside a browser. The browser has an interpreter which reads the
JavaScript program one line at a time and obeys the instructions one line at a time. This
will be important later.
What JavaScript is not
Just to clear up a few matters that cause confusion:
-
JavaScript is not Java. Both are loosely based on the C language and both have names
starting with the same four letters but these are the only connections between them.
-
JavaScript is not VBScript. Both run in a browser but VBScript won't run in browsers
other than Internet Explorer. JavaSript will run in any recent browser.
-
JavaScript is not JScript. Both are based on the ECMAScript standard but JScript is
Microsoft's interpretation and extension of the standard.
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