request-frp

(FRP stands for Functional Reactive Programming.)

request-frp is a package that provides pure wrappers around fetch and XMLHttpRequest so they can be used with types such as:

• Observable from RxJS
• Task and Either from fp-ts
• RemoteData from remote-data-ts

Primarily these wrappers are:

• TaskEither.fromFetch (uses fetch)
• ObservableEither.fromFetch (uses fetch)
• ObservableRemoteData.fromFetch (uses fetch)
• ObservableRemoteData.fromAjax (uses XMLHttpRequest)

Unlike functions such as fetch and response.json(), these functions will never throw exceptions (that also includes things like promise rejections and Observable errors). Instead, all errors are returned as objects e.g. Either.Left or RemoteData.Failure.

These functions are used heavily in production at Unsplash.

Additionally, this package provides a few convenience wrappers:

• ObservableEither.fromFetchWithJsonResponse: calling response.json() is unsafe because it can reject, so this wrapper provides a pure/safe alternative
• ObservableEither.fromFetchWithJsonResponseDecoded: decodes the response body using a given io-ts type

You can find examples in the ./src/examples directory.

Task vs Observable

Unlike Tasks, Observables can emit more than once. For example, when used with RemoteData this means they can emit Pending (i.e. loading) and then they can emit again with Failure or Success. Example.

Observables also have built-in support for cancellation via subscriptions.

If you don't care about loading states (RemoteData.Pending) and you're happy using things like AbortController, TaskEither should suffice.

ObservableRemoteData.fromFetch vs ObservableRemoteData.fromAjax

ObservableRemoteData.fromAjax includes information about the upload progress (inside RemoteData.Pending), whereas ObservableRemoteData.fromFetch does not.

To do

• Test usage with node-fetch
• Remove io-ts dependency (?)
• Remove content-type dependency (?)
• Use peer dependencies for fp-ts et al
• Publish to npm