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Create a modified request with edited properties based off of an incoming request.
Last updated Jul 6, 2026 If you want to get started quickly, click on the button below.
This creates a repository in your GitHub account and deploys the application to Cloudflare Workers.
export default {
async fetch(request) {
/**
* Example someHost is set up to return raw JSON
* @param {string} someUrl the URL to send the request to, since we are setting hostname too only path is applied
* @param {string} someHost the host the request will resolve too
*/
const someHost = "example.com";
const someUrl = "https://foo.example.com/api.js";
/**
* The best practice is to only assign new RequestInit properties
* on the request object using either a method or the constructor
*/
const newRequestInit = {
// Change method
method: "POST",
// Change body
body: JSON.stringify({ bar: "foo" }),
// Change the redirect mode.
redirect: "follow",
// Change headers, note this method will erase existing headers
headers: {
"Content-Type": "application/json",
},
// Change a Cloudflare feature on the outbound response
cf: { apps: false },
};
// Change just the host
const url = new URL(someUrl);
url.hostname = someHost;
// Best practice is to always use the original request to construct the new request
// to clone all the attributes. Applying the URL also requires a constructor
// since once a Request has been constructed, its URL is immutable.
const newRequest = new Request(
url.toString(),
new Request(request, newRequestInit),
);
// Set headers using method
newRequest.headers.set("X-Example", "bar");
newRequest.headers.set("Content-Type", "application/json");
try {
return await fetch(newRequest);
} catch (e) {
return new Response(JSON.stringify({ error: e.message }), {
status: 500,
});
}
},
};
export default {
async fetch(request): Promise<Response> {
/**
* Example someHost is set up to return raw JSON
* @param {string} someUrl the URL to send the request to, since we are setting hostname too only path is applied
* @param {string} someHost the host the request will resolve too
*/
const someHost = "example.com";
const someUrl = "https://foo.example.com/api.js";
/**
* The best practice is to only assign new RequestInit properties
* on the request object using either a method or the constructor
*/
const newRequestInit = {
// Change method
method: "POST",
// Change body
body: JSON.stringify({ bar: "foo" }),
// Change the redirect mode.
redirect: "follow",
// Change headers, note this method will erase existing headers
headers: {
"Content-Type": "application/json",
},
// Change a Cloudflare feature on the outbound response
cf: { apps: false },
};
// Change just the host
const url = new URL(someUrl);
url.hostname = someHost;
// Best practice is to always use the original request to construct the new request
// to clone all the attributes. Applying the URL also requires a constructor
// since once a Request has been constructed, its URL is immutable.
const newRequest = new Request(
url.toString(),
new Request(request, newRequestInit),
);
// Set headers using method
newRequest.headers.set("X-Example", "bar");
newRequest.headers.set("Content-Type", "application/json");
try {
return await fetch(newRequest);
} catch (e) {
return new Response(JSON.stringify({ error: e.message }), {
status: 500,
});
}
},
} satisfies ExportedHandler;
import json
from workers import WorkerEntrypoint, Response, fetch
from js import Request
from urllib.parse import urlparse
class Default(WorkerEntrypoint):
async def fetch(self, request):
some_host = "example.com"
some_url = "https://foo.example.com/api.js"
# The best practice is to only assign new_request_init properties
# on the request object using either a method or the constructor
new_request_init = {
"method": "POST", # Change method
"body": json.dumps({"bar": "foo"}), # Change body
"redirect": "follow", # Change the redirect mode
# Change headers, note this method will erase existing headers
"headers": {
"Content-Type": "application/json",
},
# Change a Cloudflare feature on the outbound response
"cf": {"apps": False},
}
# Change just the host
parsed = urlparse(some_url)
new_url = parsed._replace(netloc=some_host).geturl()
# Best practice is to always use the original request to construct the new request
# to clone all the attributes. Applying the URL also requires a constructor
# since once a Request has been constructed, its URL is immutable.
org_request = Request.new(request, new_request_init)
new_request = Request.new(new_url, org_request)
new_request.headers["X-Example"] = "bar"
new_request.headers["Content-Type"] = "application/json"
try:
return await fetch(new_request)
except Exception as e:
return Response.join({"error": str(e)}, status=500)
import { Hono } from "hono";
const app = new Hono();
app.all("*", async (c) => {
/**
* Example someHost is set up to return raw JSON
*/
const someHost = "example.com";
const someUrl = "https://foo.example.com/api.js";
// Create a URL object to modify the hostname
const url = new URL(someUrl);
url.hostname = someHost;
// Create a new request
// First create a clone of the original request with the new properties
const requestClone = new Request(c.req.raw, {
// Change method
method: "POST",
// Change body
body: JSON.stringify({ bar: "foo" }),
// Change the redirect mode
redirect: "follow" as RequestRedirect,
// Change headers, note this method will erase existing headers
headers: {
"Content-Type": "application/json",
"X-Example": "bar",
},
// Change a Cloudflare feature on the outbound response
cf: { apps: false },
});
// Then create a new request with the modified URL
const newRequest = new Request(url.toString(), requestClone);
// Send the modified request
const response = await fetch(newRequest);
// Return the response
return response;
});
// Handle errors
app.onError((err, c) => {
return err.getResponse();
});
export default app;
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description: Fetch and modify response properties which are immutable by creating a copy first. title: Modify response image: https://developers.cloudflare.com/workers/examples/modify-response/og.png?v=abf5df46729db38c
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