effect-fetch

fetch but with super-powers

• 🖇 Interceptors
• 🔐 Strongly typed errors
• 🕓 Timeouts

Install

npm install effect-fetch effect

yarn add effect-fetch effect

pnpm add effect-fetch effect

<script src="https://unpkg.com/effect-fetch/dist/index.js"></script>

effect is a required peer dependency

Example

import * as Effect from "effect/Effect";

import * as Fetch from "effect-fetch/Fetch";
import * as Result from "effect-fetch/Response";
import * as Adapter from "effect-fetch/Adapters/Fetch";

const program = Effect.gen(function* () {
  const result = yield* Fetch.fetch("/users");
  const res = yield* Result.filterStatusOk(result);
  const users = yield* Result.json(res);
});

// or
const program = Effect.gen(function* () {
  const fetch = yield* Fetch.Fetch;
  const result = yield* fetch("/users");
  const res = yield* Result.filterStatusOk(result);
  const users = yield* Result.json(res);
});

With interceptor

import * as Interceptor from "effect-fetch/Interceptor";
import { Url as BaseURL } from "effect-fetch/interceptors/Url";

const baseURL = "https://reqres.in/api";

// our list of interceptors
const interceptors = Interceptor.of(BaseURL(baseURL));

// make function that executes our interceptors
const interceptor = Interceptor.provide(
  Interceptor.make(interceptors),
  Adapter.fetch
);

// we finally make the HTTP adapter using the native Fetch API
const adapter = Fetch.effect(interceptor);

const result = await Effect.runPromise(Effect.provide(program, adapter));

POST Request

const program = Effect.gen(function* () {
  const result = yield* Fetch.fetch("/users", { method: "POST" });
  const res = yield* Result.filterStatusOk(result);
  const users = yield* Result.json(res);
});

Interceptors

effect-fetch ships with default interceptors

• Base URL
• Timeout
• Logger
• Status Filter
• Bearer and Basic authentication

Status Filter

To avoid manually forking the response into the error and success paths

const program = pipe(
  Fetch.fetch("/users"),
  // equivalent to response.ok ? response.json() : // handle not ok status
  Effect.flatMap((response) => Result.filterStatusOk(response)),
  Effect.flatMap((response) => response.json()),
  Effect.catchTag("StatusError", (error) => error)
);

We can delegate that to an interceptor. So we can decode the response body without worrying about the OK status

const program = pipe(
  Fetch.fetch("/users"),
  Effect.flatMap((response) => response.json())
);

const interceptors = Interceptor.of(StatusOK);

const interceptor = Interceptor.provide(
  Interceptor.make(interceptors),
  Adapter.fetch
);

const adapter = Fetch.effect(interceptor);

const result = await program.pipe(
  Effect.provide(adapter),
  Effect.catchTag("StatusError", (error) => error),
  Effect.runPromise
);

Writing your own interceptor

import * as Interceptor from "effect-fetch/Interceptor";

const program = Effect.gen(function* () {
  const chain = yield* Interceptor.Chain;
  const clone = chain.request.clone(); // do something with request
  const response = yield* chain.proceed(chain.request);
  // do something with response
  return response;
});

Interceptors are executed in the order which they were added (top to bottom).

Error handling

import * as Interceptor from "effect-fetch/Interceptor";
import { StatusOK } from "effect-fetch/interceptors/StatusFilter";

// Effect<string, DecodeError, Fetch>
const program = Effect.gen(function* () {
  const result = yield* Fetch.fetch("/users");
  return yield* Result.text(res);
});

const interceptors = Interceptor.empty().pipe(
  Interceptor.add(BaseURL(baseURL)),
  Interceptor.add(StatusOK) // Effect<Response, StatusError, Fetch>
);

const interceptor = Interceptor.provide(
  Interceptor.make(interceptors),
  Adapter.fetch
);

const adapter = Fetch.effect(interceptor);

// Interceptors errors get carried over into the final computation type.
// Unlike other HTTP libraries, we don't loose type information

// Effect<string, DecodeError | StatusError, Fetch>
const result = Effect.provide(program, adapter);

more examples