XHook

v1.0

Easily intercept and modify XHR request and response

Attention: XHook has been rewritten to simplify the API

With XHook, you could easily implement functionality to:

Cache requests in memory, localStorage, etc.
Insert authentication headers
- S3 Request Signing
Simulate responses
- For testing purposes, just add your test hooks and your code can remain the same
Sending Error statistics to Google Analytics
Polyfil CORS, by offloading requests to an iframe then splicing the response back in, see XDomain
Devious practical jokes
Preflight GZip compression, see XZip (In progress)

Features

Intercept and modify XHR request and response
Simulate responses transparently
Backwards compatible addEventListener removeEventListener

Future Features

Backwards compatible user controlled progress (download/upload) events

Example

Here, we're converting vowels to z's in all requests to 'example.txt':

//modify 'responseText' of 'example2.txt'
xhook.after(function(request, response) {
  if(request.url.match(/example\.txt$/)) 
    response.text = response.text.replace(/[aeiou]/g,'z');
});

Browser Support

Tested in IE8+, Chrome, Firefox, Safari

Live Demos

See the above example and more here:

http://jpillora.com/xhook

Download

Development xhook.js 7.8KB
Production xhook.min.js 3.3KB (0.8KB Gzip)

Note: It's important to include XHook first as other libraries may store a reference to XMLHttpRequest before XHook can patch it

API

`xhook`.`before`(`handler(request[, callback])`)

We can modify the request before the XHR is sent.

If our handler is asynchronous, just include the callback argument, which accepts an optional response object.

To provide a fake response, simply return or callback() a response object.

`xhook`.`after`(`handler(request, response[, callback])`)

We can read the request and modify the response before the XHR is recieved.

If our handler is asynchronous, just include the callback argument.

`request` Object

method (String)
url (String)
body (String) May implement binary data in the future
headers (Object)
timeout (Number)

`response` Object

status (Number) Required when for fake responses
statusText (String)
text (String) (XMLHttpRequest responseText)
headers (Object)
type (String) (XMLHttpRequest responseType)
xml (XML) (XMLHttpRequest responseXML)
data (Varies) (XMLHttpRequest response)

Overview

The dark red before hook is returning a response object, which will trigger the after hooks, then trigger the appropriate events, so it appears as if response came from the server.

Reference

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest

Issues

xhr instanceof XMLHttpRequest checks will return false
XHook does not attempt to resolve any browser compatibility issues. Libraries like jQuery and https://github.com/ilinsky/xmlhttprequest will attempt to do this. XHook simply proxies to and from XMLHttpRequest and ActiveXObject, so you may use any library conjunction with XHook, just make sure to load XHook first.

Old Version

Version 0.x docs and downloads can be found here

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

seanocat/xhook