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Default fetcher

By default, kweri uses the global fetch with minimal config: 
// Default behavior
const response = await fetch(url, {
  method,
  headers: body ? { 'Content-Type': 'application/json' } : {},
  body: body ? JSON.stringify(body) : undefined
})
The response is expected to be a Response-like object that kweri can call .json() on.

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Fetcher interface

interface FetcherOptions {
  method: string
  url:    string
  body?:  any     // already-parsed body object (not stringified)
}

type Fetcher = (options: FetcherOptions) => Promise<Response>

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Common patterns

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Authorization headers

const kweri = new Kweri({
  baseURL: 'https://api.example.com',
  fetcher: async ({ method, url, body }) => {
    const token = getAuthToken()  // your auth mechanism

    return fetch(url, {
      method,
      headers: {
        'Content-Type': 'application/json',
        ...(token ? { Authorization: `Bearer ${token}` } : {})
      },
      body: body ? JSON.stringify(body) : undefined
    })
  }
})

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Token refresh

const kweri = new Kweri({
  baseURL: 'https://api.example.com',
  fetcher: async ({ method, url, body }) => {
    let token = getAccessToken()

    const res = await fetch(url, {
      method,
      headers: { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' },
      body: body ? JSON.stringify(body) : undefined
    })

    // Attempt a single refresh on 401
    if (res.status === 401) {
      token = await refreshAccessToken()
      return fetch(url, {
        method,
        headers: { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' },
        body: body ? JSON.stringify(body) : undefined
      })
    }

    return res
  }
})

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Request timeout

const kweri = new Kweri({
  baseURL: 'https://api.example.com',
  fetcher: async ({ method, url, body }) => {
    const controller = new AbortController()
    const timeout = setTimeout(() => controller.abort(), 10_000)  // 10s

    try {
      return await fetch(url, {
        method,
        signal: controller.signal,
        headers: { 'Content-Type': 'application/json' },
        body: body ? JSON.stringify(body) : undefined
      })
    } finally {
      clearTimeout(timeout)
    }
  }
})

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Node.js / non-browser environments

Use any fetch-compatible library. In Node.js 18+ the global fetch is available; for older versions use node-fetch or undici: 
import { fetch } from 'undici'

const kweri = new Kweri({
  baseURL: 'https://api.example.com',
  fetcher: async ({ method, url, body }) =>
    fetch(url, {
      method,
      headers: { 'Content-Type': 'application/json' },
      body: body ? JSON.stringify(body) : undefined
    }) as unknown as Response
})

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Custom response unwrapping

If your API wraps all responses in an envelope ({ data: ..., meta: ... }), unwrap in the fetcher: 
const kweri = new Kweri({
  baseURL: 'https://api.example.com',
  fetcher: async ({ method, url, body }) => {
    const res = await fetch(url, {
      method,
      headers: { 'Content-Type': 'application/json' },
      body: body ? JSON.stringify(body) : undefined
    })

    if (!res.ok) throw new Error(`HTTP ${res.status}`)

    const envelope = await res.json()

    // Return a fake Response that kweri can call .json() on
    return new Response(JSON.stringify(envelope.data), {
      status: 200,
      headers: { 'Content-Type': 'application/json' }
    })
  }
})
The fetcher must return something kweri can call .json() on. Returning a raw parsed object won’t work — wrap it in a Response if needed.