altering-headers.md

copyright	years 2023, 2025
lastupdated	2025-12-30
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subcollection	cis

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Altering headers

{: #altering-headers}

This example illustrates how to add, change, or delete headers sent in a request or returned in a response. {: shortdesc}

You can't modify the value of certain headers, such as server, eh-cache-tag, or eh-cdn-cache-control. {: note}

export default {
	async fetch(request) {
		const response = await fetch("https://example.com");

		// Clone the response so that it's no longer immutable
		const newResponse = new Response(response.body, response);

		// Add a custom header with a value
		newResponse.headers.append(
			"x-workers-hello",
			"Hello from CIS Edge Functions",
		);

		// Delete headers
		newResponse.headers.delete("x-header-to-delete");
		newResponse.headers.delete("x-header2-to-delete");

		// Adjust the value for an existing header
		newResponse.headers.set("x-header-to-change", "NewValue");

		return newResponse;
	},
};

{: codeblock}