Molecule.dev

@molecule/api-fx-rates-openexchange

Provider bond · fx-rates · API (Node) · v1.0.2 · Apache-2.0

OpenExchangeRates FX provider — USD-pivot daily and historical JSON endpoints; free tier locked to base=USD.

npm install @molecule/api-fx-rates-openexchange

npm · Source on GitHub · Implements @molecule/api-fx-rates

How it works

@molecule/api-fx-rates-openexchange is a provider bond on the API (Node) side: it implements the fx-rates core interface (@molecule/api-fx-rates) with a concrete vendor or library behind it.

Your code calls the core; you wire this provider once at startup. Swapping vendors later is one line in that wiring, not a rewrite.

import { setProvider } from '@molecule/api-fx-rates'
import { provider } from '@molecule/api-fx-rates-openexchange'

setProvider(provider)

Works with: @molecule/api-bond, @molecule/api-fx-rates, @molecule/api-secrets

Secrets: OPENEXCHANGE_APP_ID

Reference

OpenExchangeRates FX-rates provider for molecule.dev.

Implements the import('@molecule/api-fx-rates').FxRatesProvider interface against the JSON endpoints under https://openexchangerates.org/api/. Free-tier accounts are locked to base=USD, so cross-rate requests pivot through USD; paid plans (Developer/Enterprise/Unlimited) may pass an arbitrary base.

Snapshots are cached in memory for a configurable TTL (default 1h) and, when the 'cache' bond is registered, written through to it as well.

The required OPENEXCHANGE_APP_ID env var (or config.appId) is never echoed back into error messages.

Auto-generated, AI-first package reference for the molecule.dev ecosystem. It is written to be read by coding agents as much as by people, and is generated from this package's source — edit src/index.ts JSDoc, not this file.

Quick Start

import { setProvider } from '@molecule/api-fx-rates'
import { provider } from '@molecule/api-fx-rates-openexchange'

setProvider(provider)

Type

provider

Installation

npm install @molecule/api-fx-rates-openexchange @molecule/api-bond @molecule/api-fx-rates @molecule/api-secrets

API

Interfaces

OpenExchangeFxRatesConfig

Configuration options for the OpenExchangeRates FX-rates provider.

The OpenExchangeRates API requires an app_id for every request. The default singleton reads it from OPENEXCHANGE_APP_ID. Free-tier accounts are locked to base='USD'; paid plans may override it.

interface OpenExchangeFxRatesConfig {
  /**
   * OpenExchangeRates app ID. Required at request time. If omitted, the
   * provider falls back to `process.env['OPENEXCHANGE_APP_ID']`.
   */
  appId?: string

  /**
   * Pivot currency to request from the upstream. Free-tier accounts MUST
   * leave this as the default `'USD'`; paid plans may set any currency
   * that the upstream supports. Defaults to `'USD'`.
   */
  base?: CurrencyCode

  /**
   * Base URL override. Defaults to `'https://openexchangerates.org/api'`.
   */
  baseUrl?: string

  /**
   * Request timeout in milliseconds. Defaults to `10000`.
   */
  timeout?: number

  /**
   * TTL for the in-memory cache of parsed snapshots, in milliseconds.
   * Defaults to `3_600_000` (1 hour). Set to `0` to disable internal caching.
   *
   * If the `'cache'` bond is registered, snapshots are also written through
   * to it with the equivalent TTL in seconds.
   */
  cacheTtlMs?: number
}

OpenExchangeSnapshot

A single dated snapshot of pivot rates parsed from latest.json or historical/YYYY-MM-DD.json. The pivot itself is included with rate 1.

interface OpenExchangeSnapshot {
  /**
   * The publication time of the snapshot (UTC).
   */
  asOf: Date

  /**
   * Pivot currency the snapshot is quoted against (e.g. `'USD'`).
   */
  base: CurrencyCode

  /**
   * Map from currency code to rate, where `1 base = rates[code] units of code`.
   * Always contains the `base` entry with rate `1`.
   */
  rates: Record<CurrencyCode, number>
}

Functions

snapshotFromBody(body)

Converts a LatestResponseBody into our normalised OpenExchangeSnapshot, ensuring the pivot itself is present with rate 1.

function snapshotFromBody(body: LatestResponseBody): OpenExchangeSnapshot
  • body — Parsed JSON body.

Returns: Normalised snapshot.

computeRate(snapshot, from, to)

Computes the conversion rate 1 unit of from = rate units of to from a pivot snapshot. Both sides may equal the pivot.

function computeRate(snapshot: OpenExchangeSnapshot, from: string, to: string): number
  • snapshot — The dated snapshot to read.
  • from — Source currency.
  • to — Target currency.

Returns: The conversion ratio as a plain number.

createProvider(config)

Creates an OpenExchangeRates FX-rates provider.

function createProvider(config?: OpenExchangeFxRatesConfig): FxRatesProvider
  • config — Provider configuration. appId may be omitted to fall back to process.env['OPENEXCHANGE_APP_ID'].

Returns: An FxRatesProvider backed by OpenExchangeRates.

Constants

provider

Default OpenExchangeRates FX-rates provider, lazily constructed on first access.

Reads OPENEXCHANGE_APP_ID (required) and the optional OPENEXCHANGE_FX_BASE_URL from the environment. The app_id value is never echoed back in error messages.

const provider: FxRatesProvider

fxRatesOpenexchangeSecretDefinitions

Secret definitions required by the Open Exchange Rates FX-rates bond.

const fxRatesOpenexchangeSecretDefinitions: SecretDefinition[]

Core Interface

Implements @molecule/api-fx-rates interface.

Bond Wiring

Setup function to register this provider with the core interface:

import { setProvider } from '@molecule/api-fx-rates'
import { provider } from '@molecule/api-fx-rates-openexchange'

export function setupFxRatesOpenexchange(): void {
  setProvider(provider)
}

Injection Notes

Requirements

Peer dependencies:

  • @molecule/api-bond ^1.0.1
  • @molecule/api-fx-rates ^1.0.1
  • @molecule/api-secrets ^1.0.1

Environment Variables

Runtime Dependencies

  • @molecule/api-bond
  • @molecule/api-fx-rates
  • @molecule/api-secrets

E2E Tests

Integration checklist — drive the real UI (live preview, no mocks), adapt each item to this app's actual currency/pricing screens, and check every box off one by one. This is money: a wrong rate silently corrupts every price, so verify the NUMBERS the app computes, not just that a value rendered. A box you can't check is an integration bug to fix — not a skip:

  • A known pair returns a PLAUSIBLE rate: getRate('USD', 'EUR') yields a real ratio (roughly 0.8-1.0 for USD->EUR), never 0, null, NaN, negative, or an absurd value like 1e9 — and the UI shows it as an actual number.
  • convert does the CORRECT MATH: converting 100 USD (amountMinor 10_000 cents) USD->EUR returns approximately 10_000 * rate in the target's minor units, rounded sensibly for that currency (integer cents; JPY has 0 decimals), and the UI shows that converted amount — not the untouched original.
  • Round-trip consistency: the inverse pair is reciprocal — getRate('EUR', 'USD') is approximately 1 / getRate('USD', 'EUR') — and same-currency is identity: getRate('USD', 'USD') is exactly 1 and convert(x, 'USD', 'USD') returns x unchanged.
  • Changing the selected pair changes the displayed result (USD->EUR vs USD->JPY give visibly different converted amounts) — the screen is not pinned to one hardcoded rate.
  • An unknown/unsupported code (e.g. 'ZZZ', absent from listSupportedCurrencies()) surfaces a clear error in the UI — NEVER a silent rate of 0 (which zeroes the price) or a pass-through of 1.
  • If a historical lookup is exposed (options.asOf), a past date returns that day's rate (different from latest for a volatile pair), not today's.
  • A provider/network failure surfaces gracefully (a visible error or retry) and the amount is left unconverted — the app NEVER falls back to converting at rate 0 or 1, which would corrupt the price shown or charged.
  • The provider API key stays server-side — fx-rates is server-only; the key never appears in the browser bundle, the network tab, or any client response.