svelte-check give "cannot find name 'gtag'" upon upgrading to 2.56.1 from 2.55.0

[kzw]

Describe the bug

We have a component like

<script lang="ts">
  import { page } from '$app/state';
  $: {
    if (typeof gtag !== 'undefined') {
      gtag('config', 'AW-redacted', {
        page_title: document.title,
        page_path: page.url.pathname
      });
    }
  }
</script>

<svelte:head>
  <script async src="https://www.googletagmanager.com/gtag/js?id=AW-redacted">
  </script>
  <script nonce="foobar">
    window.dataLayer = window.dataLayer || [];

    function gtag() {
      dataLayer.push(arguments);
    }

    gtag('js', new Date());
    gtag('config', 'AW-redacted');
  </script>
</svelte:head>

This component was last touched many revisions/months ago. I was prompted to upgrade svelte kit because nom audit was failing this morning. Now svelte-check is failing at this component. I believe a similar issue was posted 5 hours ago.

Reproduction

Include above component in the app

Logs

redacted/front-end/src/comp/Analytics.svelte:5:7
Error: Cannot find name 'gtag'. (ts)
    if (typeof gtag !== 'undefined') {
      gtag('config', 'AW-redacted', {
        page_title: document.title,`

System Info

System:
    OS: macOS 26.3.1
    CPU: (8) arm64 Apple M2
    Memory: 985.78 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.14.0 - /Users/me/.nvm/versions/node/v24.14.0/bin/node
    npm: 11.9.0 - /Users/me/.nvm/versions/node/v24.14.0/bin/npm
  Browsers:
    Chrome: 146.0.7680.178
    Firefox: 148.0.2
    Safari: 26.3.1
  npmPackages:
    @sveltejs/adapter-auto: ^6.0.0 => 6.1.1 
    @sveltejs/adapter-static: ^3.0.8 => 3.0.10 
    @sveltejs/kit: ^2.47.3 => 2.56.1 
    @sveltejs/vite-plugin-svelte: ^5.1.1 => 5.1.1 
    svelte: ^5.42.2 => 5.53.5 
    vite: ^6.4.1 => 6.4.2

Severity

blocking an upgrade

Additional Information

No response

[dummdidumm]

Honestly surprised this ever worked - language tools, which parses this under the hood, knows nothing about the script tag inside <svelte:head>. I suspect you changed a global d.ts file which contained this type definition, and it got updated somehow to no longer be global. Or you upgraded TypeScript while also upgrading SvelteKit and that changed behavior. I don't think SvelteKit has anything to do with this.

[elliott-with-the-longest-name-on-github]

Yeah, I'm not sure this is anything we can help with -- you need to add types for gtag in your global types.