@leancodepl/fetch-client

CQRS client using native fetch API with automatic response uncapitalization.

Features

• Native fetch API - No external HTTP dependencies, works in any JavaScript environment
• CQRS pattern - Separate queries, commands, and operations with proper typing
• Automatic uncapitalization - Response keys automatically transformed from PascalCase to camelCase
• Query abort support - Built-in AbortController for query cancellation
• Authentication - Token handling with automatic refresh and retry logic

Installation

npm install @leancodepl/fetch-client
# or
yarn add @leancodepl/fetch-client

API

mkCqrsClient(params)

Creates CQRS client using native fetch API with automatic response uncapitalization.

Parameters:

• params: MkCqrsClientParameters - Configuration object for CQRS client

Returns: Object with createQuery, createOperation, and createCommand factories

MkCqrsClientParameters

Configuration options for the CQRS client.

Properties:

• cqrsEndpoint: string - Base URL for CQRS API endpoints
• tokenProvider?: TokenProvider - Optional token provider for authentication
• fetchOptions?: Omit<RequestInit, "body" | "headers" | "method"> - Optional fetch configuration options
• tokenHeader?: string - Header name for authentication token (default: "Authorization")

Usage Examples

Basic Setup

import { mkCqrsClient } from "@leancodepl/fetch-client"

const client = mkCqrsClient({
  cqrsEndpoint: "https://api.example.com",
  tokenProvider: {
    getToken: () => Promise.resolve(localStorage.getItem("token")),
    invalidateToken: () => Promise.resolve(true),
  },
})

Query Operations

interface GetUserQuery {
  userId: string
}

interface UserResult {
  id: string
  name: string
  email: string
}

const getUser = client.createQuery<GetUserQuery, UserResult>("GetUser")

const response = await getUser({ userId: "123" })

if (response.isSuccess) {
  console.log("User:", response.result)
}

Aborting Queries

const getUser = client.createQuery<GetUserQuery, UserResult>("GetUser")

const queryPromise = getUser({ userId: "123" })

// Abort the request if needed
queryPromise.abort()

const response = await queryPromise

if (!response.isSuccess && response.isAborted) {
  console.log("Query was aborted")
}

Command Operations

interface CreateUserCommand {
  name: string
  email: string
}

const errorCodes = { EmailExists: 1, InvalidEmail: 2 } as const
const createUser = client.createCommand<CreateUserCommand, typeof errorCodes>("CreateUser", errorCodes)

const response = await createUser({ name: "John", email: "[email protected]" })

if (response.isSuccess) {
  console.log("Command result:", response.result)
}

// Using the handle method for validation
createUser.handle({ name: "John", email: "[email protected]" }).then(handler =>
  handler
    .handle("success", () => console.log("User created"))
    .handle("EmailExists", () => console.log("Email already exists"))
    .handle("failure", () => console.log("Creation failed"))
    .check(),
)

Operation Requests

interface ProcessPaymentOperation {
  orderId: string
  amount: number
}

interface PaymentResult {
  transactionId: string
  status: string
}

const processPayment = client.createOperation<ProcessPaymentOperation, PaymentResult>("ProcessPayment")

const response = await processPayment({ orderId: "order-123", amount: 99.99 })

if (response.isSuccess) {
  console.log("Transaction:", response.result.transactionId)
}

Custom Fetch Options

const client = mkCqrsClient({
  cqrsEndpoint: "https://api.example.com",
  fetchOptions: {
    credentials: "include",
  },
  tokenHeader: "X-Auth-Token",
})