Showing posts with label JavaScript Form Validation. Show all posts
Showing posts with label JavaScript Form Validation. Show all posts

Wednesday, August 29, 2012

JavaScript Form Validation


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 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:

Example

<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>

Try it yourself »


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:

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>

Try it yourself »