Tutorials - JavaScript - Lesson 7 - Functions and IF.... ELSE Commands
Functions are placed in the <head> tags of the document. They
allow the user to type in one string of code that can be referred to
(called) many times within one page. An example of a function would be:
function alertme( )
{
var ages;
ages=answer
if (ages<20)
{
alert('you are too young!');
}
else
{
alert('you are really old!');
}
}
Then, in the body section we call the function by placing it in an event
handler (in this case onClick):
<a href="#" onClick="answer=(prompt('enter
your age', ''));alertme();">click here for fun!</a>
This means that when the user clicks the link, a prompt box will appear
asking the user for their age and then the function will be called. Click
the link below for an example:
click
here for fun!
Here's what the code does:
| function alertme( ) |
Start the function and name it so it can be called
later |
| { |
Shows the beginning of the function's contents |
| var ages; |
Set up a variable called ages |
| ages=answer |
set the value of ages to answer |
if (ages<20)
|
if the value held in ages is less than 20 |
| { |
|
| alert('you are too young!'); |
alert the user that they are too young |
| } |
|
| else |
else, if the values of ages is 20 or over |
| { |
|
| alert('you are really old!'); |
Tell the user they are too old. |
| } |
|
| } |
|
As we saw before in tutorial
5, the input is gathered via a prompt box.
Functions are useful if you have many different sections of code that
need to be called at different times. If...else statements are useful for
validating user input, checking for browsers etc.
In Tutorial
8, we'll look at image a simple rollover
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| 
