jQuery plugin that enables the 'jsonpi' dataType parameter for $.ajax.
Switch branches/tags
Nothing to show
Failed to load latest commit information.
server Server is wholly contained in /server now Oct 19, 2014
.gitignore Ditch example PHP script for Node/Express server Oct 19, 2014
package.json Ditch example PHP script for Node/Express server Oct 19, 2014



jQuery plugin that enables the 'jsonpi' dataType parameter for $.ajax.

What the hell is JSONPI?

A pattern for making AJAX-like requests across subdomains. Since browsers block XmlHttpRequest across subdomains (because they have different Origins), JSONPI is a workaround that uses iframes, forms, and document.domain to achieve the same effect. Unlike JSONP, JSONPI permits the use of HTTP POSTs. See Usage for more information.

Usage / How it works

To initiate a JSONPI request:

    url: 'http://api.example.com/widgets/create.jsonpi',
    type: 'POST',
    dataType: 'jsonpi',
    params: { 'name': "Cogley's Cogs" }

This will have the effect of generating the following form and iframe DOM elements:

<iframe style="display:none" name="jQuery_iframe_1234567890">

<form action="http://api.example.com/widgets/create.jsonpi?callback=jQuery_1234567890"
    method="POST" target="jQuery_iframe_1234567890">
    <input type="hidden" name="name" value="Cogley's Cogs"/>

Notice that the form element targets the iframe. The form will be submitted, and the response loaded inside the iframe.

The server should identify that a JSONPI is being requested, and generate the following response, which is loaded inside the iframe:

<!DOCTYPE html>
        <script>document.domain = 'example.com';</script>
            window.parent.jQuery_1234567890({ 'id': '1337' });

If the parent document has the same document.domain, the iframe can execute the stored callback on the parent's window object.


The requesting page must have the same document.domain declaration in its <head>.


  • Can cause "click" sound effect in older browsers (IE)
  • Can cause address bar loading animation in some browsers
  • This will create an iframe per-request; they're not cheap


This repository includes a NodeJS server that demonstrates jquery-jsonpi in action.

$ cd jquery-jsonpi
$ npm install
$ node server

Then visit http://localhost:3000 and open your browser's developer tools to see what's going on.

Should you actually use this?

Probably not. Almost everyone is better off using CORS, or if browser support is a concern, the XDomain library.

The "JSONPI" pattern was devised during an age when CORS was just a twinkle in spec implementers eyes. Today, it's not much more than a "gee whiz neato" project that can teach you some fun things about document.domain and iframes.


Ben Vinegar (@bentlegen)