Response: body property
The body
read-only property of the Response
interface is a ReadableStream
of the body contents.
Value
A ReadableStream
, or else null
for any Response
object constructed with a null body
property, or for any actual HTTP response that has no body.
The stream is a readable byte stream, which supports zero-copy reading using a ReadableStreamBYOBReader
.
Note: Current browsers don't actually conform to the spec requirement to set the body
property to null
for responses with no body (for example, responses to HEAD
requests, or 204 No Content
responses).
Examples
Copying an image
In our simple stream pump example we fetch an image,
expose the response's stream using response.body
, create a reader using ReadableStream.getReader()
,
then enqueue that stream's chunks into a second, custom readable stream — effectively creating an identical copy of the image.
const image = document.getElementById("target");
// Fetch the original image
fetch("./tortoise.png")
// Retrieve its body as ReadableStream
.then((response) => response.body)
.then((body) => {
const reader = body.getReader();
return new ReadableStream({
start(controller) {
return pump();
function pump() {
return reader.read().then(({ done, value }) => {
// When no more data needs to be consumed, close the stream
if (done) {
controller.close();
return;
}
// Enqueue the next data chunk into our target stream
controller.enqueue(value);
return pump();
});
}
},
});
})
.then((stream) => new Response(stream))
.then((response) => response.blob())
.then((blob) => URL.createObjectURL(blob))
.then((url) => console.log((image.src = url)))
.catch((err) => console.error(err));
Creating a BYOB reader
In this example we construct a ReadableStreamBYOBReader
from the body using ReadableStream.getReader({mode: 'byob'})
. We can then use this reader to implement zero copy transfer of the response data.
async function getProducts(url) {
const response = await fetch(url);
const reader = response.body.getReader({ mode: "byob" });
// read the response
}
getProducts(
"https://mdn.github.io/learning-area/javascript/apis/fetching-data/can-store/products.json",
);
Specifications
Specification |
---|
Fetch Standard # ref-for-dom-body-body① |
Browser compatibility
BCD tables only load in the browser