vite.define cannot be used in top-level execution in client hooks in dev server

[princescar]

Describe the bug

Defined a constant in Vite config and used it in hooks.client.js, it result in ReferenceError: __SOME_THING__ is not defined.

This only affect dev server, and it only happens when used in top-level execution.

Reproduction

1. Define a constant in vite.config.js

import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
	define: {
		__SOME_THING__: { key: 'value' }
	},
	plugins: [sveltekit()]
});

2. Reference in hooks.client.js

console.log(__SOME_THING__);

3. Start the dev server

Logs

hooks.client.js:1 Uncaught (in promise) ReferenceError: __SOME_THING__ is not defined
    at hooks.client.js:1:13
(anonymous) @ hooks.client.js:1

System Info

System:
    OS: macOS 15.2
    CPU: (8) arm64 Apple M1
    Memory: 77.94 MB / 16.00 GB
    Shell: 3.7.1 - /opt/homebrew/bin/fish
  Binaries:
    Node: 22.12.0 - ~/.local/share/nvm/v22.12.0/bin/node
    Yarn: 1.22.22 - /opt/homebrew/bin/yarn
    npm: 10.9.0 - ~/.local/share/nvm/v22.12.0/bin/npm
    pnpm: 9.15.1 - /opt/homebrew/bin/pnpm
  Browsers:
    Chrome: 131.0.6778.205
    Safari: 18.2
  npmPackages:
    @sveltejs/adapter-auto: ^3.0.0 => 3.3.1 
    @sveltejs/kit: ^2.0.0 => 2.15.1 
    @sveltejs/vite-plugin-svelte: ^4.0.0 => 4.0.4 
    svelte: ^5.0.0 => 5.16.0 
    vite: ^5.4.11 => 5.4.11

Severity

annoyance

[eltigerchino]

Awaiting the client.start module import before importing client.app gives Vite a chance to define the global constant replacements before the client hooks and universal hooks modules are loaded. However, I don't think this is the right solution.

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

Lines 411 to 414 in 9a4a411

	? `Promise.all([
	import(${s(prefixed(client.start))}),
	import(${s(prefixed(client.app))})
	]).then(([kit, app]) => {

Although, I wonder why the client.start module runs runs Vite code but client.app doesn't.