GlobalFetch.fetch()

The fetch() method of the GlobalFetch interface starts the process of fetching a resource. This returns a promise that resolves to the Response object representing the response to your request.

GlobalFetch is implemented by both Window and WorkerGlobalScope — meaning that the fetch() method will be available in pretty much any context you might want to fetch resources in.

A fetch() promise will reject with a TypeError when a network error is encountered, although this usually means permissions issue or similar. An accurate check for a successful fetch() would include checking that the promise resolved, then checking that the Response.ok property has a value of true. An HTTP status of 404 does not constitute a network error.

The fetch() method is controlled by the connect-src directive of Content Security Policy rather than the directive of the resources it's retrieving.

Syntax

fetch(input, init).then(function(response) { ... });

Parameters

input

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

• A USVString containing the direct URL of the resource you want to fetch.
• A Request object.

init Optional

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

• method: The request method, e.g., GET, POST.
• headers: Any headers you want to add to your request, contained within a Headers object or ByteString.
• body: Any body that you want to add to your request: this can be a Blob, BufferSource, FormData, URLSearchParams, or USVString object. Note that a request using the GET or HEAD method cannot have a body.
• mode: The mode you want to use for the request, e.g., cors, no-cors, or same-origin.
• credentials: The request credentials you want to use for the request: omit, same-origin, or include.
• cache: The cache mode you want to use for the request: default, no-store, reload, no-cache, force-cache, or only-if-cached.

Returns

A Promise that resolves to a Response object.

Example

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 Body.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.

var myImage = document.querySelector('img');

var myRequest = new Request('flowers.jpg');

fetch(myRequest).then(function(response) {
  return response.blob();
}).then(function(response) {
  var objectURL = URL.createObjectURL(response);
  myImage.src = objectURL;
});

In our Fetch with init then Request example (see Fetch Request init live) we do the same thing except that we pass in an init object when we invoke fetch():

var myImage = document.querySelector('img');

var myHeaders = new Headers();
myHeaders.append('Content-Type', 'image/jpeg');

var myInit = { method: 'GET',
               headers: myHeaders,
               mode: 'cors',
               cache: 'default' };

var myRequest = new Request('flowers.jpg');

fetch(myRequest,myInit).then(function(response) {
  ... 
});

Note that you could also pass the init object in with the Request constructor to get the same effect, e.g.:

var myRequest = new Request('flowers.jpg',myInit);

Specifications

Browser compatibility

[1] This API is implemented behind a preference.

See also

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