Tech Blog

This week I was doing some work on a crossdomain JSON request. This was a pitty, because I had in mind, Ajax requests could be made between subdomains, but that wasn’t the case, therefore I had to come up with a solution.

Solution 1: Server-side proxy
One option we had, was a server-side proxy, but I didn’t like this solution. If you are proxying your crossdomain request through a webserver that has to handle a lot of requests per second, these requests can block other requests, because proxying is always a slow process.

Solution 2: JSONP
Then there is the JSONP method, which includes a script on the fly in the browser and this script is then evaluated. The problem however with this approach is that your JSON resources have to be rewritten as a evaluation. This evaluation is then executed and your JSON loaded in a variable.

Instead of:

{"somejsonobject":1}

you have to write:

var jsonobject = {"somejsonobject":1};
someCallback(jsonobject);

This is not very clean, because you have to decide in your remote JSON file what the variable will be named. JSONP is a method in which you give a variable and callback in the url and then the JSON will be rewritten. This solution is just not the right way, as we programmers all know why it is better to isolate logic from real data.

Solution 3: Crossdomain through flash
Then I looked at another solution that does crossdomain Ajax requests through a flash proxy. These solutions all gave a lot of problems, cause the encoding of characters was not handled properly by the Flash ExternalInterface compononent, which sended the JSON string it received to Javascript.

Solution 4: Parsing the JSON by flash
I then tried to make a solution myself that doesn’t send JSON string to Javascript, but (thanks for the idea Gert-Jan) sends the objects to Javascript. So the JSON is parsed into an object at the Actionscript side and it now all works. The project is opensourced under a MIT license and called: JSONCrossdomainRequest. It is a js file which includes a swf file in your page that can handle the requests. Please come over to GitHub and read more about how to install and use this project. The Actionscript project is also included. Good luck if you are going to use it and if you have any modifications let me know, it is a work in progress and we appreciate any help!

Project location:
http://github.com/japetheape/jsoncrossdomainrequest/tree/master

I wanted to get some data from a web service using Javascript. I looked at several Javascript classes (like this), but because the web service was running on another server it got a little troublesome. As a solution I tried to call the web service through a proxy, but that didn’t make it any easier.

Jaap suggested to take a look at NuSOAP, a -kinda old- SOAP toolkit for PHP. With an AJAX request I could call a PHP page that uses NuSOAP to consume the web service. It was actually easier then I thought it would be.

To make the AJAX call from Javascript I used Prototype and this script:

  function doRequest() {
    var url = "ajax/consume_webservice.php";
    var param1 = "value1";
    var param2 = "value2";
    var params = "param1="+ param1 +"&param2="+ param2;
 
    new Ajax.Request ( url, { method: 'POST', parameters: params,
      onComplete: onResult } );
  }
 
  function onResult( result ) {
    alert( result.responseText );
  }

The PHP file consume.php looks something like this:

< ?php
 
  $param1 = isset( $POST_['param1'] ) ? $POST_['param1'] : false;
  $param2 = isset( $POST_['param2'] ) ? $POST_['param2'] : false;
 
  // this is the only file I used from the NuSOAP project
  require_once( "nusoap.php" );
 
  $url = webserviceurl;
  $params = array( "param1" => $param1, "param2" => $param2 );
 
  $soap = new nusoap_client( $url, true, false, false, false, false, 0, 60 );
  $proxy = $soap->getProxy();
  $proxy->functionname( $params );
 
  echo $proxy->response;
 
?>

That’s all. Do a AJAX request from Javascript to a PHP page. Then the PHP page uses NuSOAP to consume the web service and returns the result. Back in Javascript you can do whatever you want with the given data.

When you try to submit a form from Javascript, using form_remote_tag, like this:

Rails:

form_remote_tag :url => {:controller => "somecontroller", :action => "} , :html => {:id => "ajax-form-1">

If you just invoke form.submit(), like this:

var form = document.getElementById('ajax-form-1');
if(form)
   form.submit();

the form will be submitted to a new page, that’s not soo ajaxy you now think. Instead use:

var form = document.getElementById('ajax-form-1');<br />
if(form.onsubmit()){
   form.submit();
}

Now your form will be submitted on the AJAX way!