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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:
* has the user left required fields empty?
* has the user entered a valid e-mail address?
* has the user entered a valid date?
* has the user entered text in a numeric field?
Required Fields
The function below checks if a required field has been left empty. If the required field is blank, an alert box alerts a message and the function returns false. If a value is entered, the function returns true (means that data is OK):
function validate_required(field,alerttxt)
{
with (field)
{
if (value==null||value=="")
{
alert(alerttxt);return false;
}
else
{
return true;
}
}
}
The entire script, with the HTML form could look something like this:
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 at least an @ sign and a dot (.). Also, the @ must not be the first character of the email address, and the last dot must at least be one character after the @ sign:
function validate_email(field,alerttxt)
{
with (field)
{
apos=value.indexOf("@");
dotpos=value.lastIndexOf(".");
if (apos<1||dotpos-apos<2)
{alert(alerttxt);return false;}
else {return true;}
}
}
The entire script, with the HTML form could look something like this:
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