Modify response
Fetch and modify response properties which are immutable by creating a copy first.
/** * @param {string} headerNameSrc Header to get the new value from * @param {string} headerNameDst Header to set based off of value in src */
const headerNameSrc = 'foo'; //"Orig-Header"
const headerNameDst = 'Last-Modified';
async function handleRequest(request) { /** * Response properties are immutable. To change them, construct a new * Response and pass modified status or statusText in the ResponseInit * object. Response headers can be modified through the headers `set` method. */ const originalResponse = await fetch(request);
// Change status and statusText, but preserve body and headers let response = new Response(originalResponse.body, { status: 500, statusText: 'some message', headers: originalResponse.headers, });
// Change response body by adding the foo prop const originalBody = await originalResponse.json(); const body = JSON.stringify({ foo: 'bar', ...originalBody }); response = new Response(body, response);
// Add a header using set method response.headers.set('foo', 'bar');
// Set destination header to the value of the source header const src = response.headers.get(headerNameSrc);
if (src != null) { response.headers.set(headerNameDst, src); console.log( `Response header "${headerNameDst}" was set to "${response.headers.get(headerNameDst)}"` ); } return response;
}
addEventListener('fetch', event => { event.respondWith(handleRequest(event.request));
});