Learning the Basics of JavaScript
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Amrit Hallan
November 29, 2006
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JavaScript
is not a full-fledged programming language so you cannot churn out
geeky applications with it. But yes, you can make your web site a lot
more interactive and dynamic if you know how to use it to your
convenience. In the initial stages, we are going to toy around with the
basic syntax. Remember one thing; you can only run Javascripts if the
individual browser allows them to run on an individual machine. Some
web surfers disable this feature because some scripts carry viruses
with them. Sticking to the ancient HTML tradition of tags and all,
here too we use tags to wake a script out of its slumber. The
appropriate tag is: <script language="JavaScript">
</script> In between lies the JavaScript code. A more refined way of using such tag is: <script language="JavaScript1.2">
</script> As
is the case with almost every software, JavaScript too has its versions
- the higher the version, the more features it supports. If you
have a fair idea of how C/C++ is done, you'll find JavaScripting to be
a cakewalk. Even otherwise, it is not such a big deal provided you have
all your logic worked out prior to getting your hands dirty. You
can fit in a JavaScript wherever you feel like, but generally,
especially if it is a collection of various functions deemed to perform
various, user-action based tasks, then it's better to write the script
before the <body> </body> tag to manage it well. We'll see
what functions are. For the sake of convenience, let's create a brand new HTML page. Insert the usual tags as: <html>
<head>
</head>
<body>
</body>
</html> For the time being, since we are not dealing with functions, we'll write the current scripts within <body> </body>. Variables:
Every programming language depends on variables as we depend on air to
breath. Every single calculation happens with the help of variables.
Variables, in computing languages, are memory addresses where you store
temporary data, to use it on and off. Take for example, this small code: <script language="JavaScript">
var first_name;
var second_name;
first_name = "Amrit";
second_name = "Hallan";
alert("Hello! My name is: " + first_name + " " + second_name);
</script> Don't worry if it looks like too much of a stress. Let's take things one by one. var
means we are trying to define a variable, and first_name means we are
giving this variable the name "first_name". It's sort of a memory
address of a particular part of the hard-disk. So now, whenever we
assign some value to first_name, it is going to be stored at that
memory address - at that spot. If we assign a new value, the old one
will be over-written. In this case, we store the value "Amrit" at the
memory address that we are addressing as "first_name". The same is with
second_name. Please note that every JavaScript statement ends
with a semi-colon - you get an error if you omit the semi-colon.
Another thing to take care of is, JavaScript is highly case-sensitive. Alert() is not same as alert(), and Amrit is not same as amrit or aMrit - they are all different in JavaScript. alert()
is a function that pops up a message window. In programming languages,
as also in mathematics, functions have parameters, and after doing
this-and-that with these parameters, they return a processed result,
whether you are happy about it or not. Even in this case, we are
supplying the function alert() with the parameter "Hello! My name is: "
+ first_name + " " + second_name such that the result is, it shows the
cumulative outcome in a popup window. If "Hello! My name is: " +
first_name + " " + second_name seems cryptic to you, I can fully
understand your feelings. There are many kinds of variables like string
variables, numeric variables, date variables, binary variables etc.
Currently we are dealing with "string variables". Strings are what they
are - strings. Strings of alphanumeric characters. Alpha means
alphabetical, and numeric means numerical, so their combination is
called alphanumeric. Now isn't that smart? So what the + (plus)
sign does is, it concatenates two or more strings, and makes them into
one string. Above, there are three strings, namely, "Hello! My name is:
", first_name that holds the strings "Amrit", and second_name that
holds the string "Hallan". Ah! I know what you are thinking. Try yourself what first_name - second_name does. Minus is not used in string concatenations. An
uncomfortable question might raise its head to challenge your
expertise: Why do we enclose "Hello! My name is: " in quotes, and leave
the other two in the open? That is because "Hello! My name is: " itself
a string, but first_name and second_name are the VARIABLES that are
holding two strings "Amrit" and "Hallan", respectively. We don't
enclose variables with quotes, but we enclose the actual strings. Till
here, things might be clear by now, so let us move to the next section,
where we learn how to display the current date on your web page. | 
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