UK postcode validation

**mrkhm** · Jun 25, 2007, 04:27

Hi

I am trying to submit a form using the code found on this page:

http://javascript.internet.com/forms...alidation.html

to achiege uk post code validation, it works, the only problem i am facing is that the form actually processes even if the post code is wrong.

i.e. even if the post code is worng and it alerts the user that the post code is wrong, when you press the "ok" button in the "alert box" the form continues processing, it should stay still, it should not process.

Please kindly advise.

I have tweaked the code a little bit by adding onclick="postit()" to my submit button area and matched the name of the form and fields etc. i.e. doucment.myformname.myfieldname etc which should not be the prblem?

Thanks in advance.

k

**HarryR** · Jun 25, 2007, 04:32

You should be returning 'false' from your postit() function to stop the form submitting.

You should also have an 'onsubmit' handler for the form.

**mrkhm** · Jun 25, 2007, 14:32

Originally Posted by HarryR

You should be returning 'false' from your postit() function to stop the form submitting.

You should also have an 'onsubmit' handler for the form.

HI Harry,

Thanks for advice, I got it to work, in addition to your advice to returning "false" as supposed to true and form handling as "on submit", i also had to add "return" to "on submit", i have pasted the code below in case anyone might need this.

In this example, my form is called "cashapplication" and my post code field in form is called "postcode", you will need to change these to match your own form and respective field names.

Code for header section:

Code HTML4Strict:

<head><SCRIPT LANGUAGE="JavaScript">
 
<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! [url]http://javascript.internet.com[/url] -->
<!-- Original code by Peter Haydon -->
<!-- [email]peter_haydon@lineone.net[/email] -->
 
<!-- Begin
function postit(){ //check postcode format is valid
 test = document.cashapplication.postcode.value; size = test.length
 test = test.toUpperCase(); //Change to uppercase
 while (test.slice(0,1) == " ") //Strip leading spaces
  {test = test.substr(1,size-1);size = test.length
  }
 while(test.slice(size-1,size)== " ") //Strip trailing spaces
  {test = test.substr(0,size-1);size = test.length
  }
 document.cashapplication.postcode.value = test; //write back to form field
 if (size < 6 || size > 8){ //Code length rule
  alert(test + " is not a valid postcode - wrong length");
  document.cashapplication.postcode.focus();
  return false;
  }
 if (!(isNaN(test.charAt(0)))){ //leftmost character must be alpha character rule
   alert(test + " is not a valid postcode - cannot start with a number");
   document.cashapplication.postcode.focus();
   return false;
  }
 if (isNaN(test.charAt(size-3))){ //first character of inward code must be numeric rule
   alert(test + " is not a valid postcode - alpha character in wrong position");
   document.cashapplication.postcode.focus();
   return false;
  }
 if (!(isNaN(test.charAt(size-2)))){ //second character of inward code must be alpha rule
   alert(test + " is not a valid postcode - number in wrong position");
   document.cashapplication.postcode.focus();
   return false;
  }
 if (!(isNaN(test.charAt(size-1)))){ //third character of inward code must be alpha rule
   alert(test + " is not a valid postcode - number in wrong position");
   document.cashapplication.postcode.focus();
   return false;
  }
 if (!(test.charAt(size-4) == " ")){//space in position length-3 rule
   alert(test + " is not a valid postcode - no space or space in wrong position");
   document.cashapplication.postcode.focus();
   return false;
   }
 count1 = test.indexOf(" ");count2 = test.lastIndexOf(" ");
 if (count1 != count2){//only one space rule
   alert(test + " is not a valid postcode - only one space allowed");
   document.cashapplication.postcode.focus();
   return false;
  }
  return true;
}
//  End -->
</script></head>

and codes for form parameter section:

Code HTML4Strict:

<form name="cashapplication" method="POST" action="***.asp" onsubmit="return postit()">

remember in my example the field in my form is named "postcode"

**Raffles** · Jun 25, 2007, 15:05

This seems like an incredibly verbose way of validating a UK postcode. Why not just use a regular expression?

I just wrote this one and it seems to work OK:

Code:

^[a-zA-Z]{1,2}[\d]{1,2}[a-zA-Z]?\s?\d[a-zA-Z]{2}$

It takes into account central London postcodes such as WC1H 9EF, which yours doesn't at the moment, and it works for postcodes with or without the space.

Also, even if it's a "valid" postcode, it doesn't mean it exists. If you really want to be accurate, you should compare it against a database of existing UK postcodes, which you need to pay for. However, limited versions (only the first part) exist, e.g. http://www.easypeasy.com/guides/article.php?article=64

**mrkhm** · Jun 25, 2007, 15:18

thanks for taking the time Raffles

**Chroniclemaster1** · Jun 25, 2007, 17:00

Is there a good reference for regular expression notations?

**Raffles** · Jun 25, 2007, 17:07

http://regular-expressions.info

Very good resource.

**Chroniclemaster1** · Jun 28, 2007, 10:15

Thanks!

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