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    Postcode finder using data supplied by royal mail

Explain more…

  Web AJAX Thoroughfare/Street Finder using .NET:

Using this Thoroughfare/Street Address Web Postcode Finder, the user:

  1. enters a postcode
  2. presses [Find Address] button
  3. has to enter the house name or number, the rest of the address is populated by the lookup



Code for PHP

This functionality is also available for PHP platform
Learn more >>
Full Address

Full Address version of this
Learn more >>

Your Web Sign Up/Checkout Page

Postcode: Postcode Finder Button
Building No/Name:
Line 1:
Line 2:
Line 3:

   Please note : This demonstration uses demonstration data unlike the live system

video  Tutorial Video : Show to add Street Address AJAX List

The above functionality can be installed in minutes in 5 easy steps:

The above Postcode Lookup for thoroughfare (Street Level) Address search functionality can be added to a .NET  capable web server in minutes, by simply dropping the supplied files into your Web project.   It is available in ASP.NET or C#.    


  • Uses AJAX to populate web page, for a smooth customer experience
  • "Out of the box" Postcode Address Search solution 
  • Very little programming required
  • Your Simply Postcode Lookup account codes are hidden from client
  • Quick to install, Simply add two files into your Web site
  • Will run on most Web servers
  • Not blocked by Pop-up blockers
  • No Data Administration Cost for you
  • Latest up to date Royal Mail data from our reliable web servers
  • Special test postcodes to test your .NET Street AJAX web postcode address finder


Web server capable of running ASP.NET code in VB/C#.   See version for PHP

Does NOT require Microsoft Version of AJAX to be loaded

How to implement in 5 steps:

Step 1 Sign up for 30 day trial

Simply use the "Sign Up for Trial" link at top right of this page to open a trial account.   We will then send you a data key, which is used to identify your account, when using the following service.

Step 2: Download the Example Code 

Simply download the example code.  The code is in the "AJAX/AJAX ASP NET Thoroughfare VB" or ""AJAX/AJAX ASP NET Thoroughfare C#" directory of our example downloads. Simply copy, into the same directory as your web page which requires Postcode Address Lookup, "SPL_AJAX_Street.js" and "SPLGetStreetAddress.aspx" files.   Download code

If you wish to have two address postcode seaches on one web page, then please use the example in the “AJAX/AJAX ASP NET Thoroughfare Address 2 Addresses VB” or "AJAX/AJAX ASP NET Thoroughfare Address 2 Addresses C#" directory. It is significantly different from the single address fill example.

Step 3 : Add reference to our JavaScript file to your page

Then on your own web page header, add the following reference to the JavaScript file you copied. 

This line is showen in the "index.html" file included in the example download, as is the rest of the code.

Reference the JavaScript file

  HTML Code in <head> in section
<script type="text/javascript" src="SPL_AJAX_Street.js"></script>

Step 4 : Add a Link, button or image to activate Postcode Lookup

Then add either a link, or button image, using the following code to activate the Postcode Lookup Web pop-up:

Example link to activate Postcode Lookup Window:

  HTML Code (in your page)
<a href= "javascript:SPLGetAddressData(document.getElementById('postcode').value)">
Lookup Address from link</a>

Example button to activate Postcode Lookup Window:

  HTML Code (in your page)
<input type=button value="Lookup Address" 
onClick= "javascript:SPLGetAddressData(document.getElementById('postcode').value)">

This could easily be changed to use an image button.  

  Note: In the above example the Postcode Text field must have an ID of "postcode"

Step 5 : Map your Address fields

Now edit the JavaScript at the end of file "SPL_AJAX_Street.js", to write the correct address lines, which result from the Postcode Lookup, back to your target web page address fields:

Example address field mappings:

  JavaScript Code (SPL_AJAX_Street.js)

Where the fields on your web page all have ID'd expressed:

<input type=text name=line1 id=line1 size=45>
<input type=text name=line2 id=line2 size=45>

When using ASP Text boxes

Simply run up your page. Right click on page, select view source, and find the ID that ASP has assigned to your ASP Textbox controls.

Probably “MainContent_” is added to start and “ASP” at end if ID you have designated. Thus we could edit the writeback section to read:

  JavaScript Code (SPL_AJAX_Full.js)
document.getElementById("MainContent_line1ASP").value = LINE1;
document.getElementById("MainContent_line2ASP").value = LINE2;
document.getElementById("MainContent_line3ASP").value = LINE3;
document.getElementById("MainContent_townASP").value = TOWN;
document.getElementById("MainContent_countyASP").value = COUNTY;
document.getElementById("MainContent_countryASP").value = COUNTRY;

Please note, if a major structure change, liek change in Master Page may change the ID's, but otherwise it should remain the same.


Step 6 : Specify the Data Key

Open an account with us. Within seconds you will then receive a data key, by e-mail, which should be entered at the top of the "SPLGetStreetAddress.aspx" file. This key will enable your account, for a 30 day evaluation period, for one postcode area.  

Identify your account:

  ASP.NET Code (SPLGetStreetAddress.aspx)

Enter Postcode "ZZ99" to use test data.   Test postcodes for various address formats.

How it Works

When the customer presses the [Find] button, then the function SPLGetAddressData is called, passing the Postcode entered in your Postcode field.   This then calls the SPLGetStreetAddress.aspx page with the Postcode in the parameters, using the xmlHttp object created when the page was opened on the browser.   This xmlHttp object provides AJAX (Asynchronous JavaScript and XML) to perform a Asynchronous call the SPLGetStreetAddress.aspx page, without a complete page refresh.

 SPLGetStreetAddress.aspx code on your web server then calls our Postcode lookup web server for the address information, adding your account information, etc.  This means the client browser never sees your account information.

When the SPLGetStreetAddress.aspx page receives address information from our server it simply relays it back to the web page (your page with address fields on the customers computer) on the client computer. 

The result of SPLGetStreetAddress.aspx is then handled by the JavaScript function SPLhandleRequestStateChange which calls SPLhandleServerResponse when fully complete.

Function SPLhandleServerResponse then reads the XML, if it contains tag "<line1>" and writes the address information to your address fields on your web page.   If the response does not contain "<line1>", because of invalid postcode entered, then it is not processed.

Why do you have to have extra pages on your server?

Reason 1

Some browsers, especially if the client has turned up the security settings, may stop the client web page talking to a server from different domain.  So by adding a page into your web domain, to relay the query to our Postcode address lookup server, removes this security problem.

Reason 2

Hides your account information from the Client Web Browser

[More information on AJAX]

[More information on AJAX Programming]

This example could easily be converted to any other server side language, since the ASP.NET pages are simply used to relay XML data from our server.  The clients side JavaScript would remain the same.