XHook

Easily intercept and modify XHR ("AJAX") request and response

With XHook, you could easily implement functionality to:

• Cache requests in memory, localStorage, etc.
• Insert authentication headers
  • S3 Request Signing, see S3 Hook
• Simulate responses
  • Create fake transparent backends for testing purposes
• Sending Error statistics to Google Analytics
• Create a client-side alternative to CORS by offloading requests to an iframe then splicing the response back in, see XDomain
• Devious practical jokes
• Supports RequiresJS and Browserify
• Preflight GZip compression, see XZip (Incomplete)

Features

• Intercept and modify XMLHttpRequest ("AJAX") request and response
• Simulate responses transparently
• Backwards compatible addEventListener removeEventListener
• Backwards compatible user controlled progress (download/upload) events

Browser Support

Support Modern Browser.

Demos

https://jpillora.com/xhook

Usage

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

Using script link to load xhook and use it, like so:

• Development xhook.js
• Production xhook.min.js
• CDN (Use latest or lock to one of the available versions)

We can also install xhook via npm.

npm install xhook

Then use ESM syntax to load xhook.

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

API

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

Modifying any property of the request object will modify the underlying XHR before it is sent.

To make the handler is asynchronous, just include the optional callback function, which accepts an optional response object.

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

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

Modifying any property of the response object will modify the underlying XHR before it is received.

To make the handler is asynchronous, just include the optional callback function.

xhook.enable()

Enables XHook (swaps out the native XMLHttpRequest class). XHook is enabled be default.

xhook.disable()

Disables XHook (swaps the native XMLHttpRequest class back in)

request Object

• method (String) (open(method,url))
• url (String) (open(method,url))
• body (String) (send(body))
• headers (Object) (Contains Name-Value pairs set with setRequestHeader(name,value))
• timeout (Number) (timeout)
• type (String) (responseType)
• withCredentials (String) (withCredentials)

response Object

• status (Number) Required when for fake responses (status)
• statusText (String) (statusText)
• text (String) (responseText)
• headers (Object) (Contains Name-Value pairs retrieved with getAllResponseHeaders())
• xml (XML) (responseXML)
• data (Varies) (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

https://www.w3.org/TR/XMLHttpRequest/

https://www.w3.org/TR/XMLHttpRequest2/

Issues

• 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, so you may use any library conjunction with XHook, just make sure to load XHook first.

• You may use synchronous XHR, though this will cause asynchronous hooks to be skipped.

Contributing

See CONTRIBUTING for instructions on how to build and run XHook locally.

License

MIT License Copyright © 2022 Jaime Pillora dev@jpillora.com