compare.js

// prototype
new Ajax.Request("/your/mom", onSuccess: function(response) { $("lightbox_content").innerHTML = response.responseJSON.contents })

// jquery
$.getJSON("/your/mom", function(json) { $("#lightbox_content").html(json.contents) })

// prototype sprinkled with a bit of love (last command out of my head)

// Helpers to make JSON requests a bit cleaner.
Ajax.Json = {
  get: function(uri, callback) {
    new Ajax.Request(uri, {
      method: 'get',
      requestHeaders: {Accept: 'application/json'},
      onSuccess: function(transport) { if (callback) callback(transport.responseJSON, transport) }
    })
  },
  post: function(uri, obj, callback, error_callback, headers) {
    new Ajax.Request(uri, {
      method: 'post',
      contentType: 'application/json',
      postBody: Object.toJSON(obj),
      requestHeaders: Object.extend({Accept: 'application/json'}, headers),
      onComplete: function(transport) {
        if (transport.request.success()) {
          if (callback) callback(transport.responseJSON, transport);
        } else {
          if (error_callback) error_callback();
        }
      }
    })
  },
  put: function(uri, obj, callback, error_callback) {
    Ajax.Json.post(uri, obj, callback, error_callback, {'X-Http-Method-Override': 'PUT'})
  },
  del: function(uri, obj, callback, error_callback) {
    Ajax.Json.post(uri, obj, callback, error_callback, {'X-Http-Method-Override': 'DELETE'})
  }
}

# ... and every JSON request just becomes so much nicer

Ajax.Json.get("/your/mom", function(json) { $("lightbox_content").update(json.contents) });