FetchBackend

Concrete HttpBackend implementation bundled with @opra/client. Uses the browser/Node.js fetch API as the transport.

OpraHttpClient and HttpFetchClient construct a FetchBackend automatically. You only interact with it directly when you want to configure defaults, register interceptors, or override its protected methods.

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Class

class FetchBackend extends HttpBackend

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Constructor

new FetchBackend(serviceUrl: string, options?: FetchBackend.Options)

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Properties

Property	Type	Description
serviceUrl	string	Normalized base URL
interceptors	FetchBackend.Interceptor[]	Active interceptors (duplicates removed)
defaults	FetchBackend.RequestDefaults	Default headers and query params merged into every request

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Protected methods

Override these to customize behavior without reimplementing the full transport.

Method	Description
send(request)	Calls fetch(request) — override to inject a custom fetch or a test double
prepareRequest(init)	Applies defaults, normalizes the URL, sets Content-Type
createResponse(init)	Constructs the HttpResponse instance
parseBody(response)	Parses the response body by Content-Type

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Body serialization

prepareRequest sets Content-Type automatically based on the body value:

Body type	Content-Type
string / number / boolean	text/plain; charset="UTF-8"
ReadableStream	application/octet-stream
Buffer	application/octet-stream
Blob	blob.type or application/octet-stream
FormData	(browser-managed multipart boundary)
Any other object	application/json;charset="UTF-8" (JSON-serialized)

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Interfaces

FetchBackend.Options

interface Options extends HttpBackend.Options {
  interceptors?: FetchBackend.Interceptor[];
  defaults?: RequestDefaults;
  document?: ApiDocument;
}

FetchBackend.RequestDefaults

Applied as baseline values to every request. Per-request values take precedence.

type RequestDefaults = {
  headers: Headers;
  params: URLSearchParams;
  cache?: RequestCache;
  credentials?: RequestCredentials;
  integrity?: string;
  keepalive?: boolean;
  mode?: RequestMode;
  redirect?: RequestRedirect;
  referrer?: string;
  referrerPolicy?: ReferrerPolicy;
  reportProgress?: boolean;
}

FetchBackend.RequestInit

interface RequestInit extends Omit<HttpBackend.RequestInit, 'body'>, globalThis.RequestInit {
  duplex?: string;
  reportProgress?: boolean;
}

FetchBackend.RequestOptions

Subset of RequestInit exposed as per-request options via .options() on HttpRequestObservable.

interface RequestOptions {
  cache?: RequestCache;
  credentials?: RequestCredentials;
  integrity?: string;
  keepalive?: boolean;
  mode?: RequestMode;
  redirect?: RequestRedirect;
  referrer?: string;
  referrerPolicy?: ReferrerPolicy;
  reportProgress?: boolean;
}

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See also

• HttpBackend — abstract base; extend to build custom transports
• HttpInterceptor — interceptors registered via FetchBackend.Options