fetch() global function - Web APIs | MDN (2024)

resource

This defines the resource that you wish to fetch. This can either be:

• A string or any other object with a stringifier — including a URL object — that provides the URL of the resource you want to fetch.
• A Request object.

options Optional

An object containing any custom settings you want to apply to the request. The possible options are:

See Also

Using the Fetch API - Web APIs | MDN

body

Any body that you want to add to your request: this can be a Blob, an ArrayBuffer, a TypedArray, a DataView, a FormData, a URLSearchParams, string object or literal, or a ReadableStream object. This latest possibility is still experimental; check the compatibility information to verify you can use it. Note that a request using the GET or HEAD method cannot have a body.

browsingTopics Experimental

A boolean specifying that the selected topics for the current user should be sent in a Sec-Browsing-Topics header with the associated request. See Using the Topics API for more details.

cache

A string indicating how the request will interact with the browser's HTTP cache. The possible values, default, no-store, reload, no-cache, force-cache, and only-if-cached, are documented in the article for the cache property of the Request object.

credentials

Controls what browsers do with credentials (cookies, HTTP authentication entries, and TLS client certificates). Must be one of the following strings:

• omit: Tells browsers to exclude credentials from the request, and ignore any credentials sent back in the response (e.g., any Set-Cookie header).
• same-origin: Tells browsers to include credentials with requests to same-origin URLs, and use any credentials sent back in responses from same-origin URLs. This is the default value.
• include: Tells browsers to include credentials in both same- and cross-origin requests, and always use any credentials sent back in responses.

  Note: Credentials may be included in simple and "final" cross-origin requests, but should not be included in CORS preflight requests.

headers

Any headers you want to add to your request, contained within a Headers object or an object literal with String values. Note that some names are forbidden.

Note: The Authorization HTTP header may be added to a request, but will be removed if the request is redirected cross-origin.

integrity

Contains the subresource integrity value of the request (e.g., sha256-BpfBw7ivV8q2jLiT13fxDYAe2tJllusRSZ273h2nFSE=).

keepalive

The keepalive option can be used to allow the request to outlive the page. Fetch with the keepalive flag is a replacement for the Navigator.sendBeacon() API.

method

The request method, e.g., "GET", "POST". The default is "GET". Note that the Origin header is not set on Fetch requests with a method of HEAD or GET. (This behavior was corrected in Firefox 65 — see Firefox bug 1508661.) Any string which is a case-insensitive match for one of the methods in RFC 9110 will be uppercased automatically. If you want to use a custom method (like PATCH), you should uppercase it yourself.

mode

The mode you want to use for the request, e.g., cors, no-cors, or same-origin.

priority

Specifies the priority of the fetch request relative to other requests of the same type. Must be one of the following strings:

high

A high priority fetch request relative to other requests of the same type.

low

A low priority fetch request relative to other requests of the same type.

auto

Automatically determine the priority of the fetch request relative to other requests of the same type (default).

redirect

How to handle a redirect response:

follow

Automatically follow redirects. Unless otherwise stated the redirect mode is set to follow.

error

Abort with an error if a redirect occurs.

manual

Caller intends to process the response in another context. See WHATWG fetch standard for more information.

referrer

A string specifying the referrer of the request. This can be a same-origin URL, about:client, or an empty string.

referrerPolicy

Specifies the referrer policy to use for the request. May be one of no-referrer, no-referrer-when-downgrade, same-origin, origin, strict-origin, origin-when-cross-origin, strict-origin-when-cross-origin, or unsafe-url.

signal

An AbortSignal object instance; allows you to communicate with a fetch request and abort it if desired via an AbortController.

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

Usage 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:

// space in "C ontent-Type"const headers = { 'C ontent-Type': 'text/xml', 'Breaking-Bad': '<3',};fetch('https://example.com/', { headers }); 

const headers = [ ['Content-Type', 'text/html', 'extra'], ['Accept'],];fetch('https://example.com/', { headers }); 

fetch('blob://example.com/', { mode: 'cors' }); 

fetch('https://user:password@example.com/'); 

fetch('https://example.com/', { referrer: './abc\u0000df' }); 

fetch('https://example.com/', { mode: 'navigate' }); 

fetch('https://example.com/', { cache: 'only-if-cached', mode: 'no-cors',}); 

fetch('https://example.com/', { method: 'CONNECT' }); 

fetch('https://example.com/', { method: 'CONNECT', mode: 'no-cors',}); 

fetch('https://example.com/', { method: 'GET', body: new FormData(),}); 

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");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 oldreqHeaders.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) => { // ...});

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);

• Fetch API
• ServiceWorker API
• HTTP access control (CORS)
• HTTP