Request: duplex property

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

See full compatibility

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The duplex read-only property of the Request interface returns the duplex mode of the request, which determines whether the browser must send the entire request before processing the response.

Value

A string with the following possible value:

"half": The browser must send the entire request before processing the response.

Notes

Although duplex can be passed as an option when constructing a Request, it is not currently exposed as a readable property on the resulting Request object in all browsers.

Examples

Checking a request's duplex mode

const stream = new ReadableStream({
  /* ... */
});
const request = new Request("/upload", {
  method: "POST",
  body: stream,
  duplex: "half", // Required for streaming requests
});

console.log(request.duplex); // "half"

Specifications

Specification
Fetch # dom-request-duplex

Browser compatibility

	desktop					mobile							server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS	Deno	Node.js
`duplex` Experimental	Chrome – Full support Chrome 131 (Release date: 2024-11-12) footnote Full support	Edge – Full support Edge 131 (Release date: 2024-11-14) footnote Full support	Firefox – No support Firefox footnote footnote See bug 1792434	Opera – Full support Opera 116 (Release date: 2025-01-08) footnote Full support	Safari – No support Safari footnote footnote See bug 245671	Chrome Android – No support Chrome Android footnote No support	Firefox for Android – No support Firefox for Android footnote footnote See bug 1792434	Opera Android – No support Opera Android footnote No support	Safari on iOS – No support Safari on iOS footnote footnote See bug 245671	Samsung Internet – No support Samsung Internet footnote No support	WebView Android – No support WebView Android footnote No support	WebView on iOS – No support WebView on iOS footnote footnote See bug 245671	Deno – No support Deno footnote No support	Node.js – No support Node.js 18.13 – 18.20 (Release date: 2023-01-06) footnote Removed in 19 and later Node.js – Full support Node.js 19.3 (Release date: 2022-12-14) footnote Full support

Tip: you can click/tap on a cell for more information.

Full support: Full support
No support: No support
: Experimental. Expect behavior to change in the future.
: See implementation notes.
: Has more compatibility info.