superagent-gmxhr

Use superagent in your Greasemonkey or Tampermonkey userscripts to make GM_xmlhttpRequest requests

Overview

Userscripts are a great way to customise your web browsing experience. Userscript webextensions such as Greasemonkey and Tampermonkey share an API that allows you to execute privileged javascript on your browser's web pages.

A commonly used API function is GM_xmlhttpRequest, which provides similar functionality to the standard browser XMLHttpRequest function, with one exception - it does not honour the browser same origin policy restrictions.
Therefore you can make requests in your userscript for resources from websites from a different origin to the currently loaded web page.

The GM_xmlhttpRequest function however has a different API to XMLHttpRequest, and is rather low-level. One higher-level library for making AJAX type requests is Superagent.
Superagent can be used in the browser to make XMLHttpRequest calls.

Using this library, Superagent can be adapted to also work with the GM_xmlhttpRequest function.

Installation

$ npm install --save superagent-gmxhr

Usage

The following steps through an end-to-end example of how to use superagent-gmxhr in your userscripts.

$ npm init
$ npm install --save superagent-gmxhr superagent browserify browserify-userscript-header

Let's create a superagent-gmxhr.meta.js file that containers the metadata for our userscript:

// ==UserScript==
// @name          Example Userscript using superagent-gmxhr
// @namespace	    https://damos.world
// @description	  A simple script demonstrating how to use superagent-gmxhr
// @version       0.0.1
// @copyright     GPL version 3; http://www.gnu.org/copyleft/gpl.html
// @grant					GM_xmlhttpRequest
// @include       *
// ==/UserScript==

Now, our userscript.js file:

var superagent = require('superagent') ;
var gmxhr = require('superagent-gmxhr') ;

/* Tell superagent to use GM_xmlhttpRequest */
gmxhr.set(superagent) ;

// Superagent will use GM_xmlhttpRequest
superagent.get('http://www.bom.gov.au/qld/forecasts/brisbane.shtml',function(err,html) {
	if(err)
		console.log('Error occurred using GM_xmlhttpRequest\n'+err) ;
	else
		console.log('Output html from GM_xmlhttpRequest'+html.text) ;
}) ;

/* Revert superagent back to using browser's built in XMLHttpRequest */
gmxhr.unset(superagent) ;


superagent.get('http://www.bom.gov.au/qld/forecasts/brisbane.shtml',function(err,html) {
	if(err)
		console.log('Error occurred using XMLHttpRequest\n'+err) ;
	else
		console.log(html) ;
}) ;

Generate our superagent-gmxhr.user.js file using browserify:

$ ./node_modules/.bin/browserify -p [ browserify-userscript-header --raw --file superagent-gmxhr.meta.js ] \
  userscript.js -o superagent-gmxhr.user.js

Install the superagent-gmxhr.user.js file into your browser using either Greasemonkey for Firefox, or Tampermonkey for Chromium-based browsers.

The output from Firefox, looks as follows. As you can see, after the gmxhr.set(superagent) call, the output shows

Output html from GM_xmlhttpRequest ...

while after the gmxhr.unset(superagent) call, the output shows

Error occurred using XMLHttpRequest ...

due to an origin error (the xhr call was made for domain www.bom.gov.au from page on domain google.com.au)

Licence

Copyright (c) 2016 Damien Clark, Damo's World Licenced under the terms of the GPLv3

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL DAMIEN CLARK BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.