Override a Set-Cookie header with a certain value

JavaScript

export default {
  async fetch(request) {
    // Receive response from the origin
    const response = await fetch(request);

    // Create a new Headers object to modify response headers
    const newHeaders = new Headers(response.headers);

    // Get all Set-Cookie headers
    const cookies = response.headers.get("Set-Cookie");
    if (cookies) {
      // Split the Set-Cookie headers
      const cookieArray = cookies.split(/,(?=\s*[^;]+=[^;]+)/g);
      const updatedCookies = cookieArray.map((cookie) => {
        // For example, replace the currency value with GBP
        if (cookie.trim().startsWith("currency=")) {
          return cookie.replace(/currency=[^;]+/, "currency=GBP");
        }
        return cookie;
      });

      // Delete the existing Set-Cookie headers
      newHeaders.delete("Set-Cookie");

      // Add the updated Set-Cookie headers individually
      updatedCookies.forEach((cookie) => {
        newHeaders.append("Set-Cookie", cookie.trim());
      });
    }

    // Return the modified response with updated headers
    return new Response(response.body, {
      status: response.status,
      headers: newHeaders,
    });
  },
};