Extract links from a webpage using HTMLRewriter

Extract links from a webpage

Bun's HTMLRewriter API extracts links from HTML. Chain CSS selectors to match the elements, text, and attributes you want to process. Then pass .transform a Response, ArrayBuffer, or string.

async function extractLinks(url: string) {
  const links = new Set<string>();
  const response = await fetch(url);

  const rewriter = new HTMLRewriter().on("a[href]", {
    element(el) {
      const href = el.getAttribute("href");
      if (href) {
        links.add(href);
      }
    },
  });

  // Wait for the response to be processed
  await rewriter.transform(response).blob();
  console.log([...links]); // ["https://bun.com", "/docs", ...]
}

// Extract all links from the Bun website
await extractLinks("https://bun.com");

Convert relative URLs to absolute

When scraping websites, you often want to convert relative URLs (like /docs) to absolute URLs:

async function extractLinksFromURL(url: string) {
  const response = await fetch(url);
  const links = new Set<string>();

  const rewriter = new HTMLRewriter().on("a[href]", {
    element(el) {
      const href = el.getAttribute("href");
      if (href) {
        // Convert relative URLs to absolute // [!code ++]
        try { // [!code ++]
          const absoluteURL = new URL(href, url).href; // [!code ++]
          links.add(absoluteURL);
        } catch { // [!code ++]
          links.add(href); // [!code ++]
        } // [!code ++]
      }
    },
  });

  // Wait for the response to be processed
  await rewriter.transform(response).blob();
  return [...links];
}

const websiteLinks = await extractLinksFromURL("https://example.com");

See HTMLRewriter.