fetch(resource)
fetch(resource, options)
Parameters
resource
This defines the resource that you wish to fetch. This can either be:
URL
object â that provides the URL of the resource you want to fetch. The URL may be relative to the base URL, which is the document's baseURI
in a window context, or WorkerGlobalScope.location
in a worker context.Request
object.options
Optional
A RequestInit
object containing any custom settings that you want to apply to the request.
A Promise
that resolves to a Response
object.
AbortError
DOMException
The request was aborted due to a call to the AbortController
abort()
method.
NotAllowedError
DOMException
Thrown if use of the Topics API is specifically disallowed by a browsing-topics
Permissions Policy, and a fetch()
request was made with browsingTopics: true
.
TypeError
Can occur for the following reasons:
RequestInit
object passed as the value of options
included properties with invalid values.In our Fetch Request example (see Fetch Request live) we create a new Request
object using the relevant constructor, then fetch it using a fetch()
call. Since we are fetching an image, we run Response.blob()
on the response to give it the proper MIME type so it will be handled properly, then create an Object URL of it and display it in an <img>
element.
const myImage = document.querySelector("img");
const myRequest = new Request("flowers.jpg");
window
.fetch(myRequest)
.then((response) => {
if (!response.ok) {
throw new Error(`HTTP error! Status: ${response.status}`);
}
return response.blob();
})
.then((response) => {
myImage.src = URL.createObjectURL(response);
});
In our Fetch Request with init example (see Fetch Request init live) we do the same thing except that we pass in an options object when we invoke fetch()
. In this case, we can set a Cache-Control
value to indicate what kind of cached responses we're okay with:
const myImage = document.querySelector("img");
const reqHeaders = new Headers();
// A cached response is okay unless it's more than a week old
reqHeaders.set("Cache-Control", "max-age=604800");
const options = {
headers: reqHeaders,
};
// Pass init as an "options" object with our headers.
const req = new Request("flowers.jpg", options);
fetch(req).then((response) => {
// â¦
});
You could also pass the init
object in with the Request
constructor to get the same effect:
const req = new Request("flowers.jpg", options);
You can also use an object literal as headers
in init
:
const options = {
headers: {
"Cache-Control": "max-age=60480",
},
};
const req = new Request("flowers.jpg", options);
The Using fetch article provides more examples of using fetch()
.
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