liaise

lee-AYZ — to act as the link between two parties.

Your API calls, minus the surprises.

Type-safe REST and GraphQL on plain fetch. Never throws. Zero dependencies. Works with any framework.

npm install liaise

Documentation · Playground · How it compares

Formerly published as @iremlopsum/apify; switching takes two steps, see MIGRATION.md.

The problem it solves

fetch is a good building block. Every project still ends up writing the same few things around it, and they are easy to get subtly wrong.

With plain fetch	liaise	See
Typing fast in a search box shows old results. A slow early search lands last.	dedupe cancels the older call.	Stale requests
Five components load the same data, or five 401s each refresh the token. That's five identical requests.	share sends one and hands everyone the answer.	Sharing identical requests
A 500 counts as success, offline throws, a hung server waits forever.	Every call returns { data, error }, and error.kind names the failure. With timeout set, a hung server becomes an error too.	Handling errors
Retries run straight past your timeout.	timeout covers the whole operation, retries included.	Deadlines
The backend changes a field and the page crashes three components later.	A schema checks the response. A bad shape is an error you handle.	Validating responses

The problem it solves shows one form submit written both ways.

Quick start

Define two endpoints, create a client, and make a call.

import { createApi, defineRequest } from 'liaise'

type User = { id: string; name: string; email: string }

// 1. Describe your endpoints. The path decides which params are required.
const getUser = defineRequest<User>()({ method: 'GET', path: '/users/:id' })
const createUser = defineRequest<User, { name: string; email: string }>()({
  method: 'POST',
  path: '/users',
})

// 2. Create the client. There is no default timeout: without one, a server
//    that never answers keeps the call waiting.
const api = createApi({
  baseUrl: 'https://api.example.com',
  requests: { getUser, createUser },
  timeout: 10_000,
})

// 3. Call it. This never throws: you always get { data, error }.
const { data, error } = await api.getUser({ id: '42' })

if (error) {
  // error.kind says what went wrong: 'http', 'network', 'timeout', ...
  console.error(error.kind, error.status)
} else {
  console.log(data.name) // data is a User here
}

// A POST sends its params as a JSON body.
const created = await api.createUser({ name: 'Grace', email: 'grace@example.com' })
if (!created.error) console.log(created.data.id)

What you just got

• The params are checked against the path, so getUser({ userId: '42' }) is a compile error.
• data is typed from defineRequest<User>.
• Nothing throws, not even when you're offline.
• Checking error first narrows data to User, so you never write data!.

Try it without installing anything in the playground.

Documentation

Everything else lives on the docs site, iremlopsum.github.io/liaise, with search.

• Getting started: the problem it solves, the quick start, and how the pieces fit together.
• Guide: defining endpoints, handling errors, sending data, reading and validating responses, deadlines and stale requests, sharing identical requests, retries, caching and logging, middleware, pagination, polling, GraphQL, and testing your code.
• Recipes: a token refresh on 401, search as you type, TanStack Query, React, a store, server loaders, a flaky backend, per-attempt timeouts, Sentry, file uploads and downloads, and a query param with a JSON body.
• Choosing liaise: when it fits and when it doesn't, how it compares with axios, ky and ofetch, and where it runs.
• Reference: every option, Result and ApiError, middleware context, liaise/testing, the exports, and behaviour in detail.

Upgrading, contributing, licence

• Upgrading. MIGRATION.md says what to change when an upgrade needs it. CHANGELOG.md lists every release. The docs site covers the latest version; for 5.1.1 and earlier, read the README at that version's tag, such as 5.1.1's.
• Contributing. Bug reports, fixes and ideas are welcome. CONTRIBUTING.md explains how to report a bug, run the tests, and the few rules a pull request is checked against.
• Licence. MIT, in LICENSE.