fetch()

The global fetch() method starts the process of fetching a resource from the network, returning a promise which is fulfilled once the response is available.

The promise resolves to the Response object representing the response to your request.

A fetch() promise only rejects when a network error is encountered (which is usually when there's a permissions issue or similar). A fetch() promise does not reject on HTTP errors (404, etc.). Instead, a then() handler must check the Response.ok and/or Response.status properties.

Note: The fetch() method's parameters are identical to those of the Request() constructor.

Explicit Backends

Internally, Fastly uses named backends to handle fetch requests, which need to be explicitly defined to enable custom HTTP origins to be fetched by the service.

This backend option is then a special Fastly-specific fetch option that is provided to the fetch() call:

fetch('https://origin.com/path', { backend: 'origin' });

Backends are configured using the Fastly service backend configuration, see the Backend documentation for more information.

Dynamic Backends

Dynamic backends are a compute feature that allow services to define backends for themselves. This is a service-level Fastly feature that must be enabled through Fastly Support.

When dynamic backends are enabled at the service level, the explicit backend option is no longer required for fetch() requests, and will instead be automatically created.

In addition, custom backend confiuration options can then also be provided through the Backend() constructor.

Syntax

fetch(resource)
fetch(resource, options)

Parameters

• resource

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

    • A string or any other object with a "toString" method.
    • A Request object.

• options optional

  • : An 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 an object literal with String values.
    • body
      • : Any body that you want to add to your request: this can be an ArrayBuffer, a TypedArray, a DataView, a URLSearchParams, string object or literal, or a ReadableStream object.
    • backend Fastly-specific
      • Fastly-specific
    • cacheOverride Fastly-specific
    • cacheKey Fastly-specific
    • fastly Fastly-specific
      • decompressGzip: boolean optional
        • Whether to automatically gzip decompress the Response or not.

Return value

A Promise that resolves to a Response object.