Function to fetch a Gist using jQuery's $.ajax and JSONP.

gist-fetch.js

// JSONP is required since gists.github.com doesn't support CORS.
// Note that it returns a Promise.

function fetch(gistid) {
  return new Promise(function(resolve, reject) {
    $.ajax('https://gist.github.com/' + gistid + '.json', {
      dataType: 'jsonp',
      cache: true
    }).done(function(gist, status, jqXhr) {
      // You can modify the gist before resolving.
      resolve(gist);
    }).fail(function(jqXhr, status, error) {
      var e = new Error('Unable to retrieve gist ' + gistid);
      reject(e);
    });
  });
}