In the last lesson we learned that we always put the code
between these tags:
<script type= "text/javascript">
<!-- //
The code goes here
//-->
</script>
While various other script attributes work fine, we should really use the following:
<script type= "text/javascript">
Because the browser always assumes your code is JavaScript, unless you tell it
different, the bare script tags work with JavaScript. But it's good practice to be
specific and tell it exactly what script you are using. Future browsers may behave
differently. For XHTML, we MUST use the tags as described.
Now for the code for the alert box. But first, let's look at the form:
< form action="">
< input
type="button" value="Press Me" onclick="alert1()" />
< /form>
The form is a normal HTML form with a button. The only difference is the onclick part. We have the code:
onclick="alert1()"
The part in blue is what JavaScript calles a function. Or, really it's the name of a
function. We know it is a function because of the () - two brackets at the end. This
always means it's a function. The function is only a name and we have to give it a some
code, or a set of instructions. This code is in the <head></head> part of the
document. Here is the code:
<script type= "text/javascript">
<!-- //
function alert1()
{
alert( "You clicked me!");
}
//-->
</script>
The actual bit of code is simple. It is:
alert("You clicked me!");
The bit in commas is the message we want the alert to display, and the line ends with a
semi-colon, as JavaScript usually does. So that's it. You have a form button. It has an
onClick which calls the function alert1() and this function is set out in the head of the
document as shown above. Don't forget the curly brackets, though!
 In old HTML, you could write onClick in
various ways. Sometimes ONCLICK. HTML is not case sensitive. It doesn't
care how you write onClick. But JavaScript is case sensitive. It does
care. When you write words inside <script> tags then you must write them correctly,
case and all. If the form is called Form, then JavaScript will not
recognise form as being the same! In future, I will write the words in
JavaScript style.
Nowadays, however, to be compatible with XHTML, we MUST write "onclick" in
lowercase letters. All attributes in the tags MUST be lowercase to be compatible with the
future.
Why not write some alert buttons for yourself and put in your own messages!
Next, let's learn how to enter a new line in JavaScript
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