Open IPython notebook from Github in NBViewer

add_gh_button.user.js

// ==UserScript==
// @name            NBViewer GitHub Button
// @description     Open IPython notebook from Github in NBViewer
// @version         0.12
// @namespace       http://telenczuk.pl
// @grant           none
// @include         http*://github.com/*
// @require         http://ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js
// ==/UserScript==

// converted from bookmarklet implemented by  Matt Davis jiffyclub 
// conversion to GreaseMonkey script by Bartosz Telenczuk
// waitForKeyElements function by Brock Adams
//    http://stackoverflow.com/questions/8281441/fire-greasemonkey-script-on-ajax-request
 
this.$ = this.jQuery = jQuery.noConflict(true);

function waitForKeyElements (
    selectorTxt,    /* Required: The jQuery selector string that
                        specifies the desired element(s).
                    */
    actionFunction, /* Required: The code to run when elements are
                        found. It is passed a jNode to the matched
                        element.
                    */
    bWaitOnce,      /* Optional: If false, will continue to scan for
                        new elements even after the first match is
                        found.
                    */
    iframeSelector  /* Optional: If set, identifies the iframe to
                        search.
                    */
)
{
    var targetNodes, btargetsFound;

    if (typeof iframeSelector == "undefined")
        targetNodes     = $(selectorTxt);
    else
        targetNodes     = $(iframeSelector).contents ()
                                           .find (selectorTxt);

    if (targetNodes  &&  targetNodes.length > 0) {
        /*--- Found target node(s).  Go through each and act if they
            are new.
        */
        targetNodes.each ( function () {
            var jThis        = $(this);
            var alreadyFound = jThis.data ('alreadyFound')  ||  false;

            if (!alreadyFound) {
                //--- Call the payload function.
                actionFunction (jThis);
                jThis.data ('alreadyFound', true);
            }
        } );
        btargetsFound   = true;
    }
    else {
        btargetsFound   = false;
    }

    //--- Get the timer-control variable for this selector.
    var controlObj      = waitForKeyElements.controlObj  ||  {};
    var controlKey      = selectorTxt.replace (/[^\w]/g, "_");
    var timeControl     = controlObj [controlKey];

    //--- Now set or clear the timer as appropriate.
    if (btargetsFound  &&  bWaitOnce  &&  timeControl) {
        //--- The only condition where we need to clear the timer.
        clearInterval (timeControl);
        delete controlObj [controlKey]
    }
    else {
        //--- Set a timer, if needed.
        if ( ! timeControl) {
            timeControl = setInterval ( function () {
                    waitForKeyElements (    selectorTxt,
                                            actionFunction,
                                            bWaitOnce,
                                            iframeSelector
                                        );
                },
                500
            );
            controlObj [controlKey] = timeControl;
        }
    }
    waitForKeyElements.controlObj   = controlObj;
}

function getUrl() {
    // here goes the code of the bookmarklet
    date=new Date();
    url_root='http://nbviewer.ipython.org/';
    url=null;
    if (location.href.search(/^https:\/\/github\.com\/.*\.ipynb$/) !== -1) {
    gh = location.href.match(/^https:\/\/github\.com\/(.*)\/(.*)\/blob\/(.*)\/(.*\.ipynb)$/);
    user = gh[1];
    repo = gh[2];
    branch = gh[3];
    file = gh[4];
    raw_url = 'raw.github.com/'+user+'/'+repo+'/'+branch+'/'+file;
    url = url_root + 'urls/' + raw_url;
    } 
    return url
};

var selector = "#files .button-group"
function addButton () {
    var newButton = document.createElement('a');
    var url = getUrl()
    if (url) {
        newButton.innerHTML = 'NBViewer';
        newButton.className = 'button minibutton'
        newButton.setAttribute('href', getUrl());
        
        var button_group = document.querySelector( selector );
        button_group.appendChild(newButton);
    }
};

waitForKeyElements(selector, addButton);