JavaScript Form Validation
JavaScript can be used to validate data in HTML forms before sending off the content to a server.Form data that typically are checked by a JavaScript could be:
- The user left required fields empty?
- The user entered a valid e-mail address?
- The user entered a valid date?
- The user entered text in a numeric field?
Required Fields
The function below checks if a field has been left empty. If the field is blank, an alert box alerts a message, the function returns false, and the form will not be submitted:
function validateForm()
{
var x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
{
alert("First name must be filled out");
return false;
}
}
The function above could be called when a form is submitted:{
var x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
{
alert("First name must be filled out");
return false;
}
}
syntax
<form name="myForm" action="demo_form.asp"
onsubmit="return validateForm()" method="post">
First name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>
First name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>
Example
<html>
<head>
<script
type="text/javascript">
function validateForm()
{
var
x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
{
alert("First name must be filled out");
return false;
}
}
</script>
</head>
<body>
<form name="myForm"
action="demo_form.asp" onsubmit="return validateForm()"
method="post">
First name: <input
type="text" name="fname">
<input type="submit"
value="Submit">
</form>
</body>
</html>
E-mail Validation
The function below checks if the content has the general syntax of an email.This means that the input data must contain an @ sign and at least one dot (.). Also, the @ must not be the first character of the email address, and the last dot must be present after the @ sign, and minimum 2 characters before the end:
function validateForm()
{
var x=document.forms["myForm"]["email"].value;
var atpos=x.indexOf("@");
var dotpos=x.lastIndexOf(".");
if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length)
{
alert("Not a valid e-mail address");
return false;
}
}
The function above could be called when a form is submitted:{
var x=document.forms["myForm"]["email"].value;
var atpos=x.indexOf("@");
var dotpos=x.lastIndexOf(".");
if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length)
{
alert("Not a valid e-mail address");
return false;
}
}
Example
<form name="myForm"
action="demo_form.asp" onsubmit="return validateForm();"
method="post">
Email: <input type="text" name="email">
<input type="submit" value="Submit">
</form>
Email: <input type="text" name="email">
<input type="submit" value="Submit">
</form>
Example
<html>
<head>
<script
type="text/javascript">
function validateForm()
{
var
x=document.forms["myForm"]["email"].value;
var atpos=x.indexOf("@");
var
dotpos=x.lastIndexOf(".");
if (atpos<1 ||
dotpos<atpos+2 || dotpos+2>=x.length)
{
alert("Not a valid e-mail address");
return false;
}
}
</script>
</head>
<body>
<form name="myForm"
action="demo_form.asp" onsubmit="return validateForm();"
method="post">
Email: <input
type="text" name="email">
<input type="submit"
value="Submit">
</form>
</body>
</html>
No comments:
Post a Comment