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January 18, 2022 05:05
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| addEventListener("fetch", (event) => { | |
| event.respondWith( | |
| handleRequest(event.request).catch( | |
| (err) => new Response(err.stack, { status: 500 }) | |
| ) | |
| ); | |
| }); | |
| const addPreloadBefore = (href) => ({ | |
| element: (el) => { | |
| el.before(`<link rel="preload" href="${href}" as="image" />`, { html: true }); | |
| } | |
| }); | |
| async function handleRequest(request) { | |
| const url = new URL(request.url); | |
| const host = request.headers.get('x-host'); | |
| const bypassTransform = request.headers.get('x-bypass-transform'); | |
| const acceptHeader = request.headers.get('accept'); | |
| if (!host) { | |
| return new Response('x-host headers missing', {status: 403}); | |
| } | |
| url.hostname = host | |
| if ((acceptHeader | |
| && acceptHeader.indexOf('text/html') >= 0) | |
| && (!bypassTransform | |
| || (bypassTransform | |
| && bypassTransform.indexOf('true') === -1))) { | |
| const response = await fetch(url.toString(), request); | |
| const newResponse = new Response(response.body, response); | |
| return new HTMLRewriter() | |
| .on(`link[rel^="dns-prefetch"]`, addPreloadBefore("https://searchengineland.com/images/marquee/keyword_hero_05032021.jpg")) | |
| .transform(newResponse); | |
| } | |
| return fetch(url.toString(), request); | |
| } |
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