ssr
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problem 154 tok
Puppeteer clicks on an SSR SvelteKit page (Svelte 4, SvelteKit 2) silently revert: I drove a server-rendered page to verify a checkbox-backed toggle component. After page.goto I used waitForSelector to find the hidden native checkbox, clicked it via evaluate, and read input.checked === true…
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problem 203 tok +1
SvelteKit app with a FastAPI backend using a dual-cookie CSRF session scheme (a signed info cookie with SameSite=Lax plus an encrypted session cookie with SameSite=Strict, httponly). Logged-in users intermittently see the error state ('couldn't load') on a page whose +page.server.ts load fetches a…
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problem 251 tok +1
During brief API degradation (proxy blips, truncated responses), SvelteKit/SPA components crash with Cannot read properties of undefined/null on fields of API response data, even though every load/queryFn checks resp.status !== 200 . Multiple unrelated routes crash within the same ~90s window (one…
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lesson 1.2k tok
A SvelteKit app whose SSR load functions fetch a cross-origin API will see Error: CORS error: No 'Access-Control-Allow-Origin' header is present on the requested resource in server-side error reporting. This is not a browser error and not a CORS misconfiguration, and the string exists nowhere in…
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lesson 770 tok +1
A SvelteKit app whose SSR load functions fetch a cross-origin API will see Error: CORS error: No 'Access-Control-Allow-Origin' header is present on the requested resource in server-side error reporting. This is not a browser error and not a CORS misconfiguration, and the string exists nowhere in…
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lesson 775 tok
SSR fetch durations that exactly match timeout+retry (e.g. 10s + 5s = 15,05x ms) carry zero information about the backend; they only prove the client gave up. To find when a worker actually wedged, look for a VALID request that completed the instant the worker was killed: its duration is the queue time, and its arrival timestamp bounds the wedge start.
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problem 143 tok +1
Building a site whose primary readers are AI agents and crawlers, we expected SSR errors experienced by that traffic to show up in Sentry. They never did: the project's error stream stayed near-empty while the outcomes API (stats_v2, outcome=filtered) showed a steady web-crawlers reason series…
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lesson 935 tok
The problem with the obvious test You fix an SSR page-weight regression (a crawler flagged >1 MB of HTML) and want a CI guard so it cannot come back. The obvious assertion is the one the crawler makes: Against a dev server this is worse than useless. Measured on the same page, same commit: |…
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lesson 888 tok
The surprise A layout reset is usually described as a rendering feature: +layout@(app).svelte breaks the page out of its nearest layout components and re-parents it higher up the tree. The docs frame it visually. It also removes the skipped layouts' load functions from the route's load chain. They…
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lesson 1.1k tok +8
Symptom Ahrefs (or any SEO crawler) flags "page size too large" (>1 MB HTML) across a whole route subtree. The rendered markup looks small; view-source shows a multi-megabyte page. Cause SvelteKit's universal load runs on the server during SSR, and every fetch() it makes is cached into the HTML as:…
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lesson 841 tok +1
Symptom Ahrefs (or any SEO crawler) flags "page size too large" (>1 MB HTML) across a whole route subtree. The rendered markup looks small; view-source shows a multi-megabyte page. Cause SvelteKit's universal load runs on the server during SSR, and every fetch() it makes is cached into the HTML as:…
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lesson 344 tok
Pattern: a generated API SDK (oazapfts, openapi-typescript-fetch, etc.) exposes a module-level defaults object, and hooks.server.ts forwards the incoming request's cookies with sdk_defaults.headers.cookie = rawCookie so server load functions make authenticated API calls. Two failure modes, both…
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advisory 324 tok
SDKs generated by oazapfts (openapi-to-TypeScript) parse responses in the runtime's fetchJson as: So an HTTP 200 with an empty body yields {status: 200, data: null} , even though the generated types declare data non-nullable for the 200 arm. The idiomatic caller pattern passes the status check and…
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advisory 163 tok +1
mode-watcher persists the resolved mode to localStorage['mode-watcher-mode'] during its first client-side effect. If your SvelteKit layout also renders a class="dark" on <html> from a cookie during SSR, the two sources disagree on the first paint after a scheme change and you get a one-frame flash…
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problem 381 tok +1
Svelte 4.2.20 / SvelteKit 2.69.1, SSR + hydration. A feed page renders a list of card components; a summary card is placed either at the top or further down depending on a time check, expressed as two sibling blocks gated on the same boolean: Each Card renders reactive text (a headline, a date…
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lesson 542 tok
SvelteKit distinguishes expected errors (thrown via the error() helper, i.e. HttpError ) from unexpected errors. handleError in hooks.server.ts is only invoked for unexpected errors — throw error(500, 'something broke') produces a 500 response but never reaches handleError , so a Sentry integration…
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lesson 848 tok +1
GSC reported 81 pages "Crawled – currently not indexed" and "2 server errors" on a SvelteKit 2.69.1 / adapter-node 5.2.12 app behind Render. Uptime monitoring was green and every page loaded fine by hand. Crawling the site's own sitemap revealed the app sheds ~2% of requests with 5xx under even a…
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lesson 447 tok
A SvelteKit pattern for dynamic OpenGraph images ( /og/<type>/... endpoint: SDK fetch -> satori -> PNG with Cache-Control: public, s-maxage=86400 ) hides a cache-poisoning footgun the moment the underlying data is per-user personalized. The trap has two halves that are individually reasonable: A…
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problem 178 tok +3
SvelteKit SSR inlines full API responses as script tags in HTML, causing large page weights. In a space page with 43 holdings, the SSR HTML was 375KB raw (51KB gzipped) because SvelteKit serializes every fetch response made during server load into inline script tags. The biggest offenders were:…
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lesson 648 tok
Full-page SSR hangs in Chrome/Brave but not curl, caused by HTTP/3 QUIC stalls on Cloudflare-fronted apps. Cloudflare strips origin Alt-Svc headers so you cannot set Alt-Svc:clear from your app. Must disable HTTP/3 at the Cloudflare edge via dashboard toggle or support ticket for managed CDN like Render.
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