![](\"./doc/img/logo.svg\"){kind=logo}
Wanted: a better logo
\n\n> A service worker router with async middleware and neato type-inference inspired by Koa\n\n\n\n#### Installation\n\n```\nnpm install -S 8track\n-- Or yarn\nyarn add 8track\n```\n\n##### TypeScript\n\nThis library is written in TypeScript, so typings are bundled.\n\n#### Basic usage\n\n```typescript\nimport { Router, handle } from '8track'\n\nconst router = new Router()\n\nrouter.all`(.*)`.use(async (ctx, next) => {\n console.log(`Handling ${ctx.event.request.method} - ${ctx.url.pathname}`)\n await next()\n console.log(`${ctx.event.request.method} - ${ctx.url.pathname}`)\n})\n\nrouter.get`/`.handle((ctx) => ctx.html('Hello, world!'))\n\nrouter.all`(.*)`.handle((ctx) => ctx.end('Not found', { status: 404 }))\n\naddEventListener('fetch', (event) => handle({ event, router }))\n```\n\n## Examples\n\n#### Add CORS headers\n\n```typescript\nimport { Router } from '8track'\n\nconst router = new Router()\n\nrouter.all`(.*)`.use(async (ctx, next) => {\n const allowedOrigins = ['https://www.myorigin.com']\n const allowedHeaders = ['Content-type', 'X-My-Custom-Header']\n const allowedMethods = ['GET', 'HEAD', 'PUT', 'POST', 'DELETE', 'PATCH']\n\n ctx.response.headers.append('Vary', 'Origin')\n ctx.response.headers.append('Access-Control-Allow-Origin', allowedOrigins.join(','))\n ctx.response.headers.append('Access-Control-Allow-Headers', allowedHeaders.join(','))\n ctx.response.headers.append('Access-Control-Allow-Methods', allowedMethods.join(','))\n ctx.response.headers.append('Access-Control-Allow-Credentials', 'true')\n\n if (ctx.req.method === 'OPTIONS') {\n return ctx.end('', { status: 204 })\n }\n\n await next()\n})\n```\n\n#### Catch all errors and display error page\n\n\n\n```typescript\nimport { Router, getErrorPageHTML } from '8track'\n\nconst router = new Router()\n\naddEventListener('fetch', (e) => {\n const res = router.getResponseForEvent(e).catch(\n (error) =>\n new Response(getErrorPageHTML(e.request, error), {\n status: 500,\n headers: {\n 'Content-Type': 'text/html',\n },\n }),\n )\n\n e.respondWith(res as any)\n})\n```\n\n#### Attach new properties to each request\n\nEach Middleware and route handler receives a new copy of the ctx object, but a special object under the `data` property is mutable and should be used to share data between handlers\n\n```typescript\ninterface User {\n id: string\n name: string\n}\n\n// Pretend this is a function that looks up a user by ID\nasync function getUserById(id: string): Promise