web api instance property
Response: bodyUsed property
Available in workers
The bodyUsed read-only property of the Response interface is a boolean value that indicates whether the body has been read yet.
Value
A boolean value.
Examples
Checking bodyUsed
This example illustrates that reading the body of a response changes the value of bodyUsed from false to true.
The example contains an empty image.
When the example’s JavaScript runs, we fetch an image and assigns the returned promise to a variable responsePromise.
When the user clicks “Use response”, we check whether the response has been used already. If it has, we print a message. If it has not, we read the response body and used it to provide a value for the image’s src attribute.
HTML
<p><button id="use">Use response</button> <button id="reset">Reset</button></p>
<p><img id="my-image" src="" width="150" /></p>
<pre id="log"></pre>
JavaScript
const useResponse = document.querySelector("#use");
const reset = document.querySelector("#reset");
const myImage = document.querySelector("#my-image");
const log = document.querySelector("#log");
const responsePromise = fetch(
"/shared-assets/images/examples/firefox-logo.svg",
);
useResponse.addEventListener("click", async () => {
const response = await responsePromise;
if (response.bodyUsed) {
log.textContent = "Body has already been used!";
} else {
const result = await response.blob();
const objectURL = URL.createObjectURL(result);
myImage.src = objectURL;
}
});
reset.addEventListener("click", () => {
document.location.reload();
});
Result
Initially there is no value for the image. If you click “Use response” once, then bodyUsed is false, so we read the response and set the image. If you then click “Use response” again, then bodyUsed is true, and we print the message.
Click “Reset” to reload the example, so you can try again.