$page is an illegal variable name

[huntabyte]

Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.

What version of ESLint are you using?

8.56.0

What version of eslint-plugin-svelte are you using?

2.36.0-next.3

What did you do?

Configuration

/** @type { import("eslint").Linter.FlatConfig } */
module.exports = {
	root: true,
	extends: [
		'eslint:recommended',
		'plugin:@typescript-eslint/recommended',
		'plugin:svelte/recommended'
	],
	parser: '@typescript-eslint/parser',
	plugins: ['@typescript-eslint'],
	parserOptions: {
		sourceType: 'module',
		ecmaVersion: 2020,
		extraFileExtensions: ['.svelte']
	},
	env: {
		browser: true,
		es2017: true,
		node: true
	},
	overrides: [
		{
			files: ['*.svelte'],
			parser: 'svelte-eslint-parser',
			parserOptions: {
				parser: '@typescript-eslint/parser'
			}
		}
	]
};

1. pnpm create svelte@latest
2. Choose Skeleton Project, Typescript, Eslint, Svelte 5
3. install dependencies
4. Realize eslint-plugin-svelte@next isn't installed, so pnpm i -D eslint-plugin-svelte@next

<!-- src/routes/+page.svelte -->
<script lang="ts">
	import { page } from "$app/stores"
	console.log($page.data) // $page is an illegal variable name.
</script>

What did you expect to happen?

$page to be a legal variable name

What actually happened?

$page is an illegal variable name. To reference a global variable called $page, use globalThis.$page(illegal-global)eslint[svelte/valid-compile](https://sveltejs.github.io/eslint-plugin-svelte/rules/valid-compile/)
let $page: Page<Record<string, string>, string | null>

4:14 error $page is an illegal variable name. To reference a global variable called $page, use globalThis.$page(illegal-global) svelte/valid-compile

Link to GitHub Repo with Minimal Reproducible Example

https://github.com/huntabyte/s5-illegal-variable-repro

Additional comments

I noticed this only occurs when using Typescript. If I go through the create svelte flow and choose "Javascript with JSDoc" everything is good.

[lyssieth]

This also happens for a custom store (in my case secret or $secret) as well.

Also Svelte 5, Eslint, TS.

[christophsturm]

is there a workaround? btw, where is the source of the next plugin, in case i want to work on a PR

[RyousukeUchino]

@christophsturm @huntabyte

I'm not entirely sure if this is correct, but I was able to find a workaround using the following method:

• eslint-plugin-svelte@2.36.0-next.12
• svelte@5.0.0-next.80

<script lang="ts">
  import { page } from '$app/stores';
  import { get } from 'svelte/store';

  const currentPagePath = get(page).url.pathname;
  const currentPageData = get(page).data
</script>
{#if currentPagePath === '/store'}
  hoge fuga
{/if}

[unlocomqx]

Is it possible to disable this error?

[jill64]

As you may already know, the @RyousukeUchino proposal may suppress warnings, but is not recommended in hot code paths.

https://svelte.dev/docs/svelte-store#get

This works by creating a subscription, reading the value, then unsubscribing. It's therefore not recommended in hot code paths.

[jill64]

@unlocomqx

The following can be used as a workaround

Disable in one line

<script>
  import { page } from '$app/stores';

  // eslint-disable-next-line svelte/valid-compile
  const currentPagePath = $page.url.pathname;
</script>

Disable in project

.eslintrc.cjs

module.exports = {
  // ...
  rules: {
    "svelte/valid-compile": "off"
  }
}

Check here for additional details
https://eslint.org/docs/latest/use/configure/rules

[ryanatkn]

The get proposal is also unsuitable as a general workaround because it's non-reactive. It subscribes and immediately unsubscribes, whereas $ subscribes and doesn't unsubscribe until the component is destroyed.

[Conduitry]

This plugin appears to be incorrectly transforming the <script> tag (perhaps via TypeScript?) before passing it to the compiler.

Something like

<script>
	import { page } from '$app/stores';
</script>

is getting transformed into

<script>import '$app/stores';
//# sourceMappingURL=module.js.map
</script>

presumably because it's only operating on the <script> tag and it thinks page is unused and it's safe to turn that into a bare import '$page/stores'.

Putting a bare reference to page; in the <script> tag seems to be a workaround for the time being.

<script>
	import { page } from '$app/stores';
	page;
</script>

gets transformed into

<script>import { page } from '$app/stores';
page;
//# sourceMappingURL=module.js.map
</script>

but the real solution is going to be fixing this transformation that the plugin does to the script tag before passing it to the Svelte compiler. If this is related to TypeScript, I think the solution is going to be to just stop running the <script> tag through TypeScript in Svelte 5, because that should be already handled by the Svelte compiler.

[unlocomqx]

I tried adding page as a global in eslint config
no luck

not a big deal though

[dummdidumm]

From @Conduitry's investigation my shot in the dark is that ts.transpileModule (or whatever the low level transpiration API is called) is called with the wrong config, where imports are not left alone and instead "treeshaken". verbatimModuleSyntax was introduced for this reason in TS and is the recommended default since TS 5.0, and leaves imports as is.

[Conduitry]

@dummdidumm In Svelte 5, is there a reason to transpile the <script> tag at all before passing it to the Svelte compiler, though?

[rChaoz]

I don't think so, the Svelte 5 compiler natively supports Typescript (now even in the template, not just the script tag).

[niemyjski]

I'm running into this as well.

[ptrxyz]

I tried setting verbatimModuleSyntax to true, but it doesn't seem to have an effect. So yes, probably it is using a wrong configuration. :/

[Alia5]

I don't think so, the Svelte 5 compiler natively supports Typescript (now even in the template, not just the script tag).

It doesn't fully support all TS features, decorators and enums among them, so there might still be a need to preproccess the files beforehand.