$page.query.get(..) returns null for prerendered pages

Describe the bug $page.query.get(...) returns null.

To Reproduce

• Repository: https://github.com/falsetru/sveltekit-test/tree/issue-1

git clone --branch issue-1 https://github.com/falsetru/sveltekit-test.git issue-1
cd issue-1
npm install
npm run build
npx sirv build/  # `npm run start` will hide the issue.

• Run above commands
• Visit http://localhost:5000/?name=abc

Expected behavior abc printed, but got null.

Information about your SvelteKit Installation:

Diagnostics

• The output of npx envinfo --system --npmPackages svelte,@sveltejs/kit,vite --binaries --browsers

  System:
    OS: Linux 5.8 Ubuntu 20.10 (Groovy Gorilla)
    CPU: (4) x64 Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
    Memory: 763.02 MB / 15.39 GB
    Container: Yes
    Shell: 5.8 - /usr/bin/zsh
  Binaries:
    Node: 12.18.2 - /usr/bin/node
    npm: 7.7.6 - ~/.npm-packages/bin/npm
  Browsers:
    Chrome: 89.0.4389.114
    Firefox: 87.0
  npmPackages:
    @sveltejs/kit: next => 1.0.0-next.67 
    svelte: ^3.29.0 => 3.37.0 
    vite: ^2.1.0 => 2.1.5 

• Your browser Google Chrome Version 89.0.4389.114 (Official Build) (64-bit)

• Your adapter @sveltejs/adapter-static

Additional context

• As a workaround, I am using new URLSearchParams(document.location.search).get('name').
• If I modify https://github.com/sveltejs/kit/blob/4a1c04a53897ac5f4831b54254b81fa0501656b4/packages/kit/src/runtime/server/page.js#L398 to

  query: new URLSearchParams(document.location.search),
  

  the issue is gone. Not sure whether it’s proper way.

[benmccann]

The issue here is that a prerendered page is a page that has already been rendered and saved as HTML. Since it’s been rendered, there’s no way on the server-side to use the query. You’d have to disable prerendering if you want to use the query on the server.

Right now, it’s pretty easy not to realize that there’s an issue there. There are a few options:

• prerendering could consider the URL as part of the page lookup key. This seems difficult though because users could potentially type any arbitrary query string and what happens if they type one that hasn’t been prerendered
• probably what I’d prefer is to have query be null or throw an exception if you try to use it during prerendering to make it more obvious that it’s something you shouldn’t do. If there’s something you want to do with the query string you should do it using the location either in onMount or behind an if (browser) check
• as https://github.com/sveltejs/kit/pull/1511 suggests we could just ignore the inability to render on the server-side and then fix up the content during hydration. This option makes me a bit nervous. While it would work and might be easier for the user, I think it also hides the fact that your content might not be what you expect when a search engine sees it. It also would not be compatible with possible additional hydration modes that could be introduced in the future. E.g. if you consider the way that React does hydration where the DOM content is not updated, but event listeners are simply added, then this solution would not work

update: I think Rich’s thinking largely aligns with my proposed solution given his comment here: https://github.com/sveltejs/kit/pull/1511#issuecomment-850907659

[benmccann]

@benmccann Your solution should only work within the browser because document is not defined outside the browser (i.e. when adapter-static is prerendering everything)

I have no idea what you’re referring to as being my solution because I have not commented on this thread at all