Old JavaScript docs links go to the utility they pointed at

site/public/_routes.json

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+{
+  "version": 1,
+  "include": ["/utilities", "/utilities/", "/pt-br/utilities", "/pt-br/utilities/", "/libs/javascript/", "/pt-br/libs/javascript/"],
+  "exclude": []
+}

site/public/_worker.js

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+// Cloudflare Pages runs this only for the paths in _routes.json; every other request is a static
+// file. The old JavaScript docs (docsify) kept a section in the query string: /utilities?id=isvalidcpf
+// for a function, /pt-br/utilities?id=cep-e-endereço for a heading. A _redirects rule cannot read
+// a query string, so this sends each to its utility's page, from /legacy-ids.json (see
+// src/lib/legacy-ids.ts). Without a known id: /utilities goes to the library's page as before, and
+// the library's page is served as is.
+export default {
+  async fetch(request, env) {
+    const url = new URL(request.url);
+    const pt = url.pathname.startsWith('/pt-br/');
+    const prefix = pt ? '/pt-br' : '';
+    const id = url.searchParams.get('id');
+    if (id) {
+      const res = await env.ASSETS.fetch(new URL('/legacy-ids.json', url));
+      if (res.ok) {
+        const to = (await res.json())[pt ? 'pt-BR' : 'en'][id.toLowerCase()];
+        if (to) return Response.redirect(new URL(prefix + to, url).toString(), 301);
+      }
+    }
+    if (/^(\/pt-br)?\/utilities\/?$/.test(url.pathname)) return Response.redirect(new URL(`${prefix}/libs/javascript/${url.search}`, url).toString(), 301);
+    return env.ASSETS.fetch(request);
+  },
+};

site/src/app/legacy-ids.json/route.ts

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+// /legacy-ids.json: where each anchor of the old JavaScript docs is now (see lib/legacy-ids.ts).
+// public/_worker.js reads it for the old URLs that carry an ?id=.
+import { legacyIds } from '@/lib/legacy-ids';
+
+export const dynamic = 'force-static';
+
+export function GET() {
+  return Response.json(legacyIds());
+}

site/src/lib/legacy-ids.ts

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+// Where the old JavaScript docs' anchors are now. That site (docsify) put a section in the query
+// string: /utilities?id=isvalidcpf for a function, /utilities?id=cep-e-endereço for a heading. Those
+// URLs reach public/_worker.js, which answers with a 301 to the utility's page from this map.
+import { loadSpecs, loadStatus } from './data';
+import { type Locale, pick } from './i18n';
+import { slug } from './prose';
+
+// The old page's section headings that are not a utility's title, in both languages.
+const SECTIONS: Record<string, string> = {
+  'cep-and-address': 'cep',
+  'cep-e-endereço': 'cep',
+  pix: 'pix-key',
+  'nf-e-key': 'nfe-key',
+  'chave-de-nf-e': 'nfe-key',
+  'nfs-e-key': 'nfse-key',
+  'chave-de-nfs-e': 'nfse-key',
+  pis: 'pis',
+  'processo-jurídico': 'legal-process',
+  'bank-accounts-and-banks': 'bank-account',
+  'contas-bancárias-e-bancos': 'bank-account',
+  'currency-numbers-and-dates-in-words': 'currency',
+  'moeda-números-e-datas-por-extenso': 'currency',
+  'states-and-municipalities': 'state',
+  'estados-e-municípios': 'state',
+  'holidays-and-business-days': 'date',
+  'feriados-e-dias-úteis': 'date',
+  'voter-id-título-de-eleitor': 'voter-id',
+  'título-de-eleitor': 'voter-id',
+  'certidão-civil-registry-certificate': 'certidao',
+  'cei-cno-and-caepf': 'cei',
+  'cei-cno-e-caepf': 'cei',
+  'gtin-product-barcode': 'gtin',
+  'gtin-código-de-barras-de-produto': 'gtin',
+  'inscrição-estadual-ie': 'ie',
+  'e-mail': 'email',
+  'credit-card': 'credit-card',
+  'cartão-de-crédito': 'credit-card',
+  'professional-registration': 'registro-profissional',
+  'registro-profissional': 'registro-profissional',
+  vin: 'vin',
+};
+
+/** Old anchor (lowercase) → the page, without the language prefix, in each language. */
+export function legacyIds() {
+  const status = loadStatus();
+  const js = status?.libs?.javascript?.functions ?? {};
+  const specs = loadSpecs() as any[];
+  const ids = new Set(specs.map((s) => s.id));
+  const out = {} as Record<Locale, Record<string, string>>;
+  for (const locale of ['en', 'pt-BR'] as Locale[]) {
+    const m: Record<string, string> = {};
+    for (const [key, id] of Object.entries(SECTIONS)) if (ids.has(id)) m[key] = `/utils/${id}/`;
+    for (const spec of specs) {
+      m[spec.id] ??= `/utils/${spec.id}/`;
+      for (const l of ['en', 'pt-BR'] as Locale[]) m[slug(pick(spec.title, l))] ??= `/utils/${spec.id}/`;
+      for (const op of spec.operations) {
+        const symbol = js[op.fnId]?.symbol;
+        if (symbol) m[symbol.toLowerCase()] = `/utils/${spec.id}/#${slug(pick(op.label, locale))}`;
+      }
+    }
+    out[locale] = m;
+  }
+  return out;
+}