Why do you have to learn
about fancy string handling
before getting into the joyous world of
cookies? Well, it turns out
that cookies are strings. To store visitor
information, you
have to first build a special cookie string. And then to
read the
information when the visitor returns, you have to decode the
cookie string. To create and interpret these strings, you have to know
your way around JavaScript's string library.
var normal_monkey = "I am a Good!<br>";
document.writeln("Normal monkey " + normal_monkey);
var bold_monkey = normal_monkey.bold();
document.writeln("Bold monkey " + bold_monkey);
The statement:
var bold_monkey = normal_monkey.bold();
Is the same as the
statement:
var bold_monkey = "<b>" + normal_monkey + "</b>";
The first version
just looks neater. One of the many
methods of the
string object is bold, and it's
sort of silly. Less silly are the methods
indexOf, charAt,
substring, and split, which actually
get inside strings and see what they're made of. Let's look at
indexOf
first.
indexOf
The indexOf finds the
location of a set of characters inside a string and
tells you where the
substring starts. If the string doesn't contain the
substring,
indexOf returns "-1." Here are some
examples:
- var the_word = "monkey";
- Let's start
with the word "monkey."
- var location_of_m =
the_word.indexOf("m");
- The location_of_m will be "0," because
that's the starting position of a string.
- var
location_of_o = the_word.indexOf("o");
- The location_of_o
will be "1."
- var location_of_key =
the_word.indexOf("key");
- location_of_key is "3" because
the substring "key" starts with "k," which is position three in the word
"monkey."
- var location_of_y =
the_word.indexOf("y");
- The location_of_y is
"5."
- var cheeky =
the_word.indexOf("q");
- The cheeky is "-1" because there's no
letter "q" in the word "monkey."
A more realistic use of
indexOf is:
var the_email = prompt("What's your email address?", "");
var the_at_is_at = the_email.indexOf("@");
if (the_at_is_at == -1)
{
alert("You loser, email addresses must
have @ signs in them.");
}
This little scrap of code asks
users for their email address,
and then checks to see if it's a valid
address. If the address
doesn't contain an @ sign, it can't be valid.
Enter indexOf, which checks for "@" in the string.
charAt
The charAt finds out what
letter is at a certain
position inside a string. Here it is in
action:
var the_word = "monkey";
var the_first_letter = the_word.charAt(0);
var the_second_letter = the_word.charAt(1);
var the_last_letter = the_word.charAt(the_word.length-1);
After
this, the_first_letter is "m,"
the_second_letter is
"o," and
the_last_letter is "y."
Note that you can find
out how many letters are in a word using the
length property of the
string. In this case, the_word is "monkey,"
so
the_word.length is "6." Don't forget that the
first
character of a string is at position "0" (as in charAt(0)), so the
last letter will be in position length-1, which is why the last
line features the_word.length-1.
Before going over
substring and split, let's do
an exercise with
charAt and indexOf.
String Exercise 1
Your task is to write a script that will determine whether
the
last letter of a word is a vowel or a consonant. You can do it
in a
clever way, using both indexOf and charAt. Of course you
could do it in a much less clever way without indexOf, but
remember: the clever monkey gets the golden banana.
Here's an
example of
it
working. When you've finished the exercise, or nearly died trying,
learn how it's done or double-check your work against my solution. Or, if
you're so pleased with your solution that you don't want to sully your mind
with mine, feel free to carry on with the string-a-thon.
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