use DATA_SUFFIX constant

packages/kit/src/runtime/client/client.js

@@ -10,6 +10,7 @@ import Root from '__GENERATED__/root.svelte';
 import { nodes, dictionary, matchers } from '__GENERATED__/client-manifest.js';
 import { HttpError, Redirect } from '../control.js';
 import { stores } from './singletons.js';
+import { DATA_SUFFIX } from '../../constants.js';
 
 const SCROLL_KEY = 'sveltekit:scroll';
 const INDEX_KEY = 'sveltekit:index';
@@ -1364,7 +1365,7 @@ let data_id = 1;
  */
 async function load_data(url, invalid) {
  const data_url = new URL(url);
- data_url.pathname += `${url.pathname.endsWith('/') ? '' : '/'}__data.js`;
+ data_url.pathname = url.pathname.replace(/\/$/, '') + DATA_SUFFIX;
  data_url.searchParams.set('__invalid', invalid.map((x) => (x ? 'y' : 'n')).join(''));
  data_url.searchParams.set('__id', String(data_id++));
 

packages/kit/src/runtime/server/page/index.js

@@ -9,6 +9,7 @@ import { error, json } from '../../../exports/index.js';
 import { compact } from '../../../utils/array.js';
 import { normalize_error } from '../../../utils/error.js';
 import { load_data, load_server_data } from './load_data.js';
+import { DATA_SUFFIX } from '../../../constants.js';
 
 /**
  * @typedef {import('./types.js').Loaded} Loaded
@@ -103,7 +104,7 @@ export async function render_page(event, route, page, options, state, resolve_op
  }
 
  const should_prerender_data = nodes.some((node) => node?.server);
- const data_pathname = `${event.url.pathname.replace(/\/$/, '')}/__data.js`;
+ const data_pathname = event.url.pathname.replace(/\/$/, '') + DATA_SUFFIX;
 
  // it's crucial that we do this before returning the non-SSR response, otherwise
  // SvelteKit will erroneously believe that the path has been prerendered,