HomeDHTML Page 4 - Rough Guide To The DOM (part 2)
Well-Formed - DHTML
Now that you know the theory behind the new DOM, it's time totake off the gloves and get your hands dirty. In this article, find out howthe new rules apply to old favourites like image swaps, form validation andframe navigation, and then learn how to use ordinary JavaScript to add andremove elements from the document tree on the fly.
Another very popular use of JavaScript is form validation - verifying the data entered into an online form. In the next example, I'll be using the DOM and some simple JavaScript to ensure that the checkbox is ticked and the email address entered into the text field is in the correct format. Here's the form
<html>
<head>
</head>
<body>
<form action="somescript.cgi" method="post" onSubmit="return check();">
Email address:
<br>
<input id="email" type="text" name="email" size="30">
<br>
<input id="spam_me" type="Checkbox" name="spam_me">Yes, I want you to send
me megabytes of useless advertisements via email. I love buying crummy
products from people who probably flunked kindergarten.
<br>
<input type="submit">
</form>
</body>
</html>
and here's the validation script.
<script language="JavaScript">
function checkEmail()
{
// get to the field
var obj = document.getElementById("email");
// value of field
var str = obj.value;
// define pattern to match email address
var pattern =
/^([a-zA-Z0-9])+([\.a-zA-Z0-9_-])*@([a-zA-Z0-9_-])+(\.[a-zA-Z0-9_-]+)+/;
// match the string to the pattern
var flag = pattern.test(str);
if(!flag)
{
alert ("Please enter a valid email address");
return false;
}
else
{
return true;
}
}
function checkSpam()
{
// get to the field
var obj = document.getElementById("spam_me");
// checkbox ticked?
if (obj.checked)
{
return true;
}
else
{
alert ("Please check the box");
return false;
}
}
function check()
{
// perform validation and submit form if all is well
if(checkEmail() && checkSpam())
{
return true;
}
else
{
return false;
}
}
</script>
As you can see, the form is submitted only after
receiving a positive (true) result from the JavaScript function check(). This function, in turn, calls the functions checkEmail() and checkSpam(),which first obtain references to their respective form elements and then check their values for validity.
This article copyright Melonfire 2001. All rights reserved.
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