Userscript to add a 'flag' button to deleted Stack Exchange posts

Question

As part of my daily routine, I flag deleted questions on Stack Exchange. Usually, I see something like this:

And to flag a deleted post that I can't see, I have to open Postman and fake the POST request for flagging. This takes a lot of time and is inconvenient.

I want a userscript/extension that:

• Adds a flag button to deleted post 404 pages
• Ideally brings up the standard flag dialog, but it absolutely must allow me to input custom text for a 'requires moderator attention' flag. I don't really care about other flag types, so the standard dialog isn't required
• Ideally it wouldn't require me to authenticate with the API, instead using the standard POST requests available inside the page (with my fkey).

Is there a script that can do this?

Answer 1

// ==UserScript==
// @name         Flag Link for Deleted Messages
// @namespace    http://github.com/
// @version      0.1
// @description  Eh.
// @author       Madara Uchiha
// @include        /http:\/\/.+\.stackexchange.com/
// @include        /http:\/\/.+\.stackoverflow.com/
// @include        /http:\/\/stackoverflow.com/
// @include        /http:\/\/askubuntu.com/
// @include        /https:\/\/.+\.stackexchange.com/
// @include        /https:\/\/.+\.stackoverflow.com/
// @include        /https:\/\/stackoverflow.com/
// @include        /https:\/\/askubuntu.com/
// @grant        none
// ==/UserScript==

if ($('h1:contains(Page Not Found)').length > 0) {
    var postId = document.location.href.match(/questions\/(\d+)\//)[1];
    var $a = $('<a />', {
        text: 'Flag this question',
        css : {
            float: 'right'
        }
    });
    var $spinner = $('<img />', {
        src: 'http://i.imgur.com/YPmA6Jk.gif',
        css: {
            position: 'fixed',
            top     : 0,
            right   : 0
        }
    });
    $a.on('click', function () {
        var flagMessage = prompt('Enter flag message here.');
        $.post('/flags/posts/' + postId + '/add/PostOther', {
            fkey     : StackExchange.options.user.fkey,
            otherText: flagMessage
        }, hideSpinner);
        showSpinner()
    });
    $('#mainbar-full .subheader').append($a);
    $('#mainbar-full .subheader').append($spinner);

    $spinner.hide();

    function showSpinner() {
        $spinner.show();
    }

    function hideSpinner() {
        $spinner.hide('slow');
    }
}

Above userscript adds a link to the right of the header of every 404 page that allows you to flag the question with a custom flag via a simple prompt() call.