Seen here: https://gist.github.com/1042725 (extracted for use with gasoline gem)

gistfile1.js

/*
  Display Gists inline.

  This responder illustrates using Propane's requestJSON service to request
  JSON from remote (non-authenticated) servers and have the results passed
  to a callback of your choosing.
*/

var displayGists = true;
if (displayGists) {

  Campfire.GistExpander = Class.create({
    initialize: function(chat) {
      this.chat = chat;
      var messages = this.chat.transcript.messages;
      for (var i = 0; i < messages.length; i++) {
        this.detectGistURL(messages[i]);
      }
    },

    detectGistURL: function(message) {
      /* we are going to use the messageID to uniquely identify our requestJSON request
         so we don't check pending messages */
      if (!message.pending() && message.kind === 'text') {
        var links = message.bodyElement().select('a:not(image)');
        if (links.length != 1) {
          return;
        }
        var href = links[0].getAttribute('href');
        var match = href.match(/^https?:\/\/gist.github.com\/[A-Za-z0-9]+\/?$/);
        if (!match) return;
        var id = match[0].replace(/^https?:\/\/gist.github.com\/([A-Za-z0-9]+)\/?$/, '$1');

        window.propane.requestJSON(message.id(), 'https://api.github.com/gists/' + id, 'window.chat.gistexpander', 'onEmbedDataLoaded', 'onEmbedDataFailed');
      }
    },

    onEmbedDataLoaded: function(messageID, data) {
      var message = window.chat.transcript.getMessageById(messageID);
      if (!message) return;

      var files = data['files'];

      for (f in files) {
        var file = files[f];
        var content = file['content'].replace(/&/g,'&amp;').
                        replace(/>/g,'&gt;').
                        replace(/</g,'&lt;').
                        replace(/"/g,'&quot;').
                        match(/^.*([\n\r]+|$)/gm).
                        slice(0,5).
                        join("");
        var link = file['raw_url'];
        var file_name = file['filename'];
        message.resize((function() {
          message.bodyCell.insert({bottom: '<div style="width:100%; margin-top:5px; padding-top: 5px; border-top:1px dotted #ccc;border-bottom:1px dotted #ccc;"><a href="' + link + '" target="_blank">' + file_name  + '</a><pre><code>' + content + '</code></pre></div>'});
        }).bind(this));
      }
    },

    onEmbedDataFailed: function(messageID) {
      /* No cleanup required, we only alter the HTML after we get back a succesful load from the data */
    },

    onMessagesInsertedBeforeDisplay: function(messages) {
      for (var i = 0; i < messages.length; i++) {
        this.detectGistURL(messages[i]);
      }
    },

    onMessageAccepted: function(message, messageID) {
      this.detectGistURL(message);
    }
  });

  Campfire.Responders.push("GistExpander");
  window.chat.installPropaneResponder("GistExpander", "gistexpander");
}