fetchmap

fetchmap

Non-throwing fetch wrapper

Getting started

npm i fetchmap

Description

This is a simple wrapper for a fetch-like function that catches all possible exceptions and returns a 'success or failure' wrapped value. It takes an object to map response.status to <T, U>(body: U, response: Response) => T transform and standard fetch arguments.

Example

// server code
import express from 'express'

express()
  .get('/json', (_, res) => {
    res.json({ some: 'data' })
  })
  .listen(5005)

// client code
import { createFetchmap } from 'fetchmap'
import fetch from 'node-fetch'

const success = <T>(value: T) => ({ tag: 'success', success: value } as const)

const fetchmap = createFetchmap(fetch)

const mock_data_validator = (data: unknown) => success(data)

const json_success = await fetchmap(
  { ok: { json: mock_data_validator } },
  'https://localhost:5005/json'
)
expect(json_success).toEqual({ tag: 'success', success: { some: 'data' } })

const json_success_only_200 = await fetchmap(
  { 200: mock_data_validator },
  'https://localhost:5005/json'
)
expect(json_success_only_200).toEqual({ tag: 'success', success: { some: 'data' } })

const invalid_url_failure = await fetchmap({}, '1234')
expect(invalid_url_failure).toEqual({
  tag: 'failure',
  failure: { clientError: new TypeError('Only absolute URLs are supported') }
})

const not_found_error_with_request_init = await fetchmap(
  { notOk: ({ status }) => status },
  'https://localhost:5005/invalid',
  { method: 'POST', credentials: 'include' }
)
expect(not_found_error_with_request_init).toEqual({ tag: 'failure', failure: { serverError: 404 } })

Usage

See test or playground

Misc

ts-railway - compatible result library