fitdays-api

Unofficial TypeScript SDK for the FitDays API.

Covers email/phone login and data sync (syncFromServer), with full typings for the response — including automatic JSON parsing of the ext_data field on weight measurements.

import { FitDaysClient } from 'fitdays-api'

const client = new FitDaysClient({ region: 'us' })
await client.login('foo@example.com', 'my-password')
const sync = await client.syncAll()
console.log(sync.data.weight_list[0].weight_kg)

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Contents

1. Install & requirements
2. Quick start
3. API — FitDaysClient
4. Sync response types
5. Error handling
6. Recipes
7. Project layout
8. Scripts
9. Disclaimer

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Install & requirements

• Node.js ≥ 22 (the SDK is pure ESM with NodeNext and uses the built-in fetch).
• TypeScript ≥ 5.5 (optional — works fine in plain JS too).

npm install
npm run build

---

Quick start

import { FitDaysClient } from 'fitdays-api'

const client = new FitDaysClient({ region: 'us' })

// Login (the plaintext password is hashed internally)
const session = await client.login('foo@example.com', 'my-password')
console.log('uid:', session.uid)

// Pull ~6 years of data
const sync = await client.syncAll()
console.log(`${sync.data.weight_list.length} measurements`)

// Custom window (unix-seconds; startTime is the UPPER bound)
const now = Math.floor(Date.now() / 1000)
const week = await client.syncFromServer({
  endTime: now - 7 * 86400,
  startTime: now,
})

---

API — FitDaysClient

Constructor

new FitDaysClient(opts?: ClientOptions)

option	default	description
region	'us'	'us' | 'eu' | 'cn' — picks the API host
baseUrl	derived from region	overrides the host (useful for tests or new hosts)
country	'US'	sent as the country query param
language	'en'	sent as the language query param
deviceModel	'AndroidSDKbuiltforarm64-6.0'	sent as the device_model query param
clientId	generated (uppercase MD5 of UUID)	identifies the client "device"
fetchImpl	globalThis.fetch	inject for tests or to use undici / node-fetch

Public properties

client.baseUrl       string — auto-updated on a 302 redirect
client.clientId      readonly string
client.country       readonly string
client.deviceModel   readonly string
client.language      readonly string
client.session       Session | null — populated by login

To "log in" without calling login() (e.g. reusing a saved token):

client.session = { token: '...', uid: 12345, refreshToken: '...' }

Methods

interface FitDaysClient {
  login(email: string, password: string): Promise<Session>
  loginWithPhone(phone: string, password: string): Promise<Session>
  syncFromServer(opts: { endTime: number, startTime: number }): Promise<ApiResponse<SyncFromServerData>>
  syncAll(): Promise<ApiResponse<SyncFromServerData>>
  request<T>(path: string, body?: unknown): Promise<ApiResponse<T>>
}

Every method throws FitDaysApiError when the response carries an error code.

request<T>(path, body)

Low-level helper for any endpoint that uses the same signing scheme. It pulls the token and client_id from the current session automatically:

const res = await client.request<{ items: unknown[] }>('api/some/endpoint', { foo: 1 })

Handles code: 302 redirects automatically (updates client.baseUrl and replays the request).

syncFromServer({ endTime, startTime })

Heads-up: by server convention, startTime is the most-recent bound and endTime is the oldest (both in unix-seconds). syncAll() is shorthand for [now - ~6 years, now].

Each weight_list[i].ext_data is JSON-decoded into a typed object before it reaches you — no need to call JSON.parse yourself.

---

Sync response types

import type {
  SyncFromServerData,
  WeightRecord,
  WeightExtData,
  HeightRecord,
  Device,
  BindDevice,
  AccountInfo,
  User,
} from 'fitdays-api'

type	content
SyncFromServerData	root object with 13 lists + account
AccountInfo	account record (uid, email, server_id, configs, …) + sub-users
User	sub-user (suid, nickname, sex, birthday, height, photo)
Device / BindDevice	physical device and its account binding
WeightRecord	one body-composition measurement
WeightExtData	parsed shape of ext_data inside each WeightRecord
HeightRecord	one height measurement

Lists with too few observed samples stay typed as Record<string, unknown>[] (RulerRecord, BalanceRecord, GravityRecord, ImpedanceRecord, HrRecord, SkipRecord, Product). Once you capture a populated response, tighten them in src/types/sync.ts.

If you need the un-parsed shape, use WeightRecordRaw / SyncFromServerDataRaw (same fields, but ext_data stays as a string). The helpers parseWeightRecord and parseSyncFromServerData are exported as well.

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Error handling

FitDaysApiError extends Error is thrown when:

• The API returns a code other than 0 or 200.
• The response body is not JSON.
• The server returned a redirect (302) without a domain field.
• A successful login response is missing token and uid.

import { FitDaysApiError } from 'fitdays-api'

try {
  await client.login(email, password)
} catch (err) {
  if (err instanceof FitDaysApiError) {
    console.error('code', err.code, 'response', err.response)
  } else {
    throw err
  }
}

---

Recipes

Reuse a saved session

const client = new FitDaysClient({ region: 'us' })
client.session = JSON.parse(await readFile('session.json', 'utf8'))
await client.syncAll()

Filter recent, non-deleted measurements for the active user

const sync = await client.syncAll()
const activeUid = sync.data.account.active_suid
const meAndRecent = sync.data.weight_list
  .filter((w) => w.suid === activeUid && w.is_deleted === 0)
  .sort((a, b) => b.measured_time - a.measured_time)

Custom fetch for request logging

const verboseFetch: typeof fetch = (input, init) => {
  console.log('→', input)
  return fetch(input, init)
}
const client = new FitDaysClient({ fetchImpl: verboseFetch })

---

Project layout

src/
├── client/
│   └── fitdays-client.ts   FitDaysClient
├── constants/
│   ├── api.ts              APP_VER, REGION_HOSTS, FULL_SYNC_WINDOW_SECONDS, …
│   └── sign.ts             SIGN_SECRET, PASSWORD_SALT
├── errors/
│   └── api-error.ts        FitDaysApiError
├── scripts/
│   ├── test-sync.ts        run a real sync (reads .env)
│   └── verify-sign.ts      checks the signer against a known vector
├── tests/                  unit tests (node:test)
├── types/
│   ├── api.ts              ApiResponse, LoginData
│   ├── client.ts           Region, ClientOptions, Session
│   ├── sign.ts             SignParams
│   └── sync.ts             syncFromServer response types
├── utils/
│   ├── crypto.ts           md5Hex, hashPassword, newClientId, newRequestId
│   ├── encode.ts           javaUrlEncode
│   ├── parse-sync.ts       parseWeightRecord, parseSyncFromServerData
│   └── sign.ts             buildSign
└── fitdays-api.ts          entry point — re-exports the public API

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Scripts

script	what it does
npm run build	compiles with tsc to dist/
npm run lint	ESLint (typescript-eslint + perfectionist + stylistic) with --fix
npm test	compiles + runs the native Node tests with coverage. Fails below 90% lines/funcs or 80% branches
npm run verify-sign	checks the signer against a known vector
npm run test:sync	full login + sync against the real server (reads FITDAYS_EMAIL / FITDAYS_PASSWORD from .env); writes the response to sync-response.json

To use test:sync, create a .env file (already in .gitignore):

FITDAYS_EMAIL=foo@example.com
FITDAYS_PASSWORD=my-password

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Disclaimer

This SDK is not affiliated with or endorsed by FitDays / Icomon. Use at your own risk and respect the service's ToS.