| copyright |
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| lastupdated | 2026-06-02 | ||
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| subcollection | cis |
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{: #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}
addEventListener('fetch', event => {
event.respondWith(handleRequest(event.request))
})
async function handleRequest(request) {
const response = await fetch(request)
// 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-CIS-Functions-Hello", "Hello from CIS Workers")
// 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}