let addHeaders = {

 "Access-Control-Allow-Origin": "*"

}



let removeHeaders = [



]



addEventListener("fetch", event => {

 event.respondWith(fetchAndApply(event.request))

})



async function fetchAndApply(request) {

 // Fetch the original page from the origin

 let response = await fetch(request)



 // Make response headers mutable

 response = new Response(response.body, response)



 // Set each header in addHeaders

 Object.keys(addHeaders).map(function(name, index) {

 response.headers.set(name, addHeaders[name])

 })



 // Delete each header in removeHeaders

 removeHeaders.forEach(function(name){

 response.headers.delete(name)

 })



 // Return the new mutated page

 return response

}

addEventListener('fetch', event => {

 event.respondWith(handleRequest(event.request))

})



/**

 * @param {Request} request

 */

async function handleRequest(request) {

 const response = await fetch(request)

 var headers = new Headers();

 for (var kv of response.headers.entries()) {

 headers.append(kv[0], kv[1]);

 }

 const url = request.url

 headers.set("Content-Type", get_content_type(url))

 headers.set("x-julia-test", "edited headers!")

 response.headers = headers

 return new Response(response.body, {

 status: response.status,

 statusText: response.statusText,

 headers: headers})

 return response

}



function get_content_type(url) {

 if (url.endsWith(".svg")) {

 return "image/svg+xml"

 } else if (url.endsWith(".png")) {

 return "image/png"

 } else if (url.endsWith(".jpg")) {

 return "image/jpg"

 } else if (url.endsWith(".css")) {

 return "text/css"

 } else if (url.endsWith(".pdf")) {

 return "application/pdf"

 } else if (url.endsWith(".js")) {

 return "application/javascript"

 } else if (url.endsWith(".json")) {

 return "application/json"

 } else if (url.endsWith(".xml")) {

 return "text/xml"

 } else {

 return "text/html; charset=UTF-8"

 }

}