From b1ac745d70b700389b12bb977d9f1e1e8eb6972a Mon Sep 17 00:00:00 2001
From: Oli Sturm <oliver+commitsigning@oliversturm.com>
Date: Fri, 24 Apr 2026 18:04:54 +0100
Subject: [PATCH] add js-fp3

---
 js-fp3/application/accountApp.js    |  47 +++++++++++
 js-fp3/domain/account.js            |  72 +++++++++++++++++
 js-fp3/domain/money.js              |  16 ++++
 js-fp3/index.js                     |  54 +++++++++++++
 js-fp3/infrastructure/repository.js |  69 ++++++++++++++++
 js-fp3/library/logging.js           |  59 ++++++++++++++
 js-fp3/library/result.js            | 119 ++++++++++++++++++++++++++++
 js-fp3/package.json                 |  10 +++
 8 files changed, 446 insertions(+)
 create mode 100644 js-fp3/application/accountApp.js
 create mode 100644 js-fp3/domain/account.js
 create mode 100644 js-fp3/domain/money.js
 create mode 100644 js-fp3/index.js
 create mode 100644 js-fp3/infrastructure/repository.js
 create mode 100644 js-fp3/library/logging.js
 create mode 100644 js-fp3/library/result.js
 create mode 100644 js-fp3/package.json

diff --git a/js-fp3/application/accountApp.js b/js-fp3/application/accountApp.js
new file mode 100644
index 0000000..9d29091
--- /dev/null
+++ b/js-fp3/application/accountApp.js
@@ -0,0 +1,47 @@
+import { bind, ok, tap, tapError, pipe } from '../library/result.js';
+import { output, outputError } from '../library/logging.js';
+import { withdraw } from '../domain/account.js';
+import { createMoney } from '../domain/money.js';
+
+/**
+ * @typedef {import('../infrastructure/repository.js').Repository} Repository
+ * @typedef {import('../domain/account.js').Account} Account
+ * @typedef {import('../domain/account.js').AccountError} AccountError
+ * @typedef {import('../infrastructure/repository.js').AppError} AppError
+ * @typedef {import('../library/result.js').Result<Account, AccountError>} AccountResult
+ * @typedef {(accountId: string, amount: number) => AccountResult} WithdrawMoneyFn
+ * @typedef {import('../library/result.js').Result<WithdrawMoneyFn, AppError>} CreateWithdrawMoneyResult
+ */
+
+/**
+ * @param {string} src
+ * @param {string} msg
+ * @returns {<T, E>(result: import('../library/result.js').Result<T, E>) => import('../library/result.js').Result<T, E>}
+ */
+const log = (src, msg) => (result) =>
+  tap((x) => output(src, msg)(x))(tapError((e) => outputError(src, e))(result));
+
+/**
+ * @param {string} src
+ * @param {(x: T) => string} renderText
+ * @returns {<T, E>(result: import('../library/result.js').Result<T, E>) => import('../library/result.js').Result<T, E>}
+ */
+const logWith = (src, renderText) => (result) =>
+  tap((x) => output(src, renderText(x))(x))(tapError((e) => outputError(src, e))(result));
+
+/**
+ * @param {Repository} repo
+ * @returns {CreateWithdrawMoneyResult}
+ */
+export const createWithdrawMoney = (repo) =>
+  ok((accountId, amount) =>
+    pipe(
+      repo.loadAccount(accountId),
+      log('App load', 'Account loaded'),
+      log('App exec wdrwl', `[App] Executing withdrawal of ${amount.toFixed(2)}...`),
+      bind((account) => withdraw(account, createMoney(amount))),
+      logWith('App wdrwl done', (a) => `Withdrawal applied. New balance: ${a.balance.amount.toFixed(2)}`),
+      bind(repo.saveAccount),
+      log('App acc svd', '[App] Account persisted.')
+    )
+  );
diff --git a/js-fp3/domain/account.js b/js-fp3/domain/account.js
new file mode 100644
index 0000000..0590bd8
--- /dev/null
+++ b/js-fp3/domain/account.js
@@ -0,0 +1,72 @@
+import { ok, fail } from '../library/result.js';
+
+/**
+ * @typedef {Object} Account
+ * @property {string} id
+ * @property {import('./money.js').Money} balance
+ */
+
+/** @typedef {{ type: 'OpeningBalanceMustBeNonNegative' }} OpeningBalanceMustBeNonNegative */
+/** @typedef {{ type: 'AmountMustBePositive' }} AmountMustBePositive */
+/** @typedef {{ type: 'InsufficientBalance', balance: import('./money.js').Money, amount: import('./money.js').Money }} InsufficientBalance */
+/** @typedef {{ type: 'AccountNotFound', accountId: string }} AccountNotFound */
+
+/** @typedef {OpeningBalanceMustBeNonNegative | AmountMustBePositive | InsufficientBalance | AccountNotFound} AccountError */
+
+/**
+ * @type {OpeningBalanceMustBeNonNegative}
+ */
+export const openingBalanceMustBeNonNegative = { type: 'OpeningBalanceMustBeNonNegative' };
+
+/**
+ * @type {AmountMustBePositive}
+ */
+export const amountMustBePositive = { type: 'AmountMustBePositive' };
+
+/**
+ * @param {import('./money.js').Money} balance
+ * @param {import('./money.js').Money} amount
+ * @returns {InsufficientBalance}
+ */
+export const insufficientBalance = (balance, amount) => ({
+  type: 'InsufficientBalance',
+  balance,
+  amount,
+});
+
+/**
+ * @param {string} accountId
+ * @returns {AccountNotFound}
+ */
+export const accountNotFound = (accountId) => ({
+  type: 'AccountNotFound',
+  accountId,
+});
+
+/**
+ * @param {string} id
+ * @param {import('./money.js').Money} openingBalance
+ * @returns {import('../library/result.js').Result<Account, AccountError>}
+ */
+export const openAccount = (id, openingBalance) =>
+  openingBalance.amount < 0
+    ? fail(openingBalanceMustBeNonNegative)
+    : ok({ id, balance: openingBalance });
+
+/**
+ * @param {Account} account
+ * @param {import('./money.js').Money} amount
+ * @returns {import('../library/result.js').Result<Account, AccountError>}
+ */
+export const withdraw = (account, amount) => {
+  if (amount.amount <= 0) {
+    return fail(amountMustBePositive);
+  }
+  if (account.balance.amount < amount.amount) {
+    return fail(insufficientBalance(account.balance, amount));
+  }
+  return ok({
+    ...account,
+    balance: { amount: account.balance.amount - amount.amount },
+  });
+};
diff --git a/js-fp3/domain/money.js b/js-fp3/domain/money.js
new file mode 100644
index 0000000..b83ed64
--- /dev/null
+++ b/js-fp3/domain/money.js
@@ -0,0 +1,16 @@
+/**
+ * @typedef {Object} Money
+ * @property {number} amount
+ */
+
+/**
+ * @param {number} amount
+ * @returns {Money}
+ */
+export const createMoney = (amount) => ({ amount });
+
+/**
+ * @param {Money} money
+ * @returns {string}
+ */
+export const formatMoney = (money) => money.amount.toFixed(2);
diff --git a/js-fp3/index.js b/js-fp3/index.js
new file mode 100644
index 0000000..fab48db
--- /dev/null
+++ b/js-fp3/index.js
@@ -0,0 +1,54 @@
+import { randomUUID } from 'crypto';
+import { catchResult, bind, tap, tapError, mapError, pipe } from './library/result.js';
+import { output, outputError } from './library/logging.js';
+import { createInMemoryRepository, innerAccountError } from './infrastructure/repository.js';
+import { openAccount } from './domain/account.js';
+import { createMoney } from './domain/money.js';
+import { createWithdrawMoney } from './application/accountApp.js';
+
+/**
+ * @param {string} src
+ * @param {string} msg
+ * @returns {<T, E>(result: import('./library/result.js').Result<T, E>) => import('./library/result.js').Result<T, E>}
+ */
+const log = (src, msg) => (result) =>
+  tap((x) => output(src, msg)(x))(tapError((e) => outputError(src, e))(result));
+
+/**
+ * @param {string} src
+ * @param {(x: T) => string} renderText
+ * @returns {<T, E>(result: import('./library/result.js').Result<T, E>) => import('./library/result.js').Result<T, E>}
+ */
+const logWith = (src, renderText) => (result) =>
+  tap((x) => output(src, renderText(x))(x))(tapError((e) => outputError(src, e))(result));
+
+console.log('[js-fp3] Starting withdraw money demo...');
+
+const accountId = randomUUID();
+
+// Try changing this to 250 to see an error being handled
+const withdrawalAmount = 100;
+
+pipe(
+  catchResult(
+    createInMemoryRepository,
+    (ex) => ({ type: 'RepositoryCreationFailed', message: ex.message })
+  ),
+  bind((repo) =>
+    pipe(
+      createWithdrawMoney(repo),
+      bind((withdrawMoney) =>
+        pipe(
+          openAccount(accountId, createMoney(200)),
+          logWith('js-fp3 seed', (account) => `Seeding account ${account.id} with opening balance ${account.balance.amount.toFixed(2)}`),
+          bind(repo.saveAccount),
+          log('js-fp3 exec', `Executing withdrawal ${withdrawalAmount.toFixed(2)} from account ${accountId}`),
+          bind(() => withdrawMoney(accountId, withdrawalAmount)),
+          logWith('js-fp3 new balance', (account) => `New balance is ${account.balance.amount.toFixed(2)}`),
+          mapError((ae) => innerAccountError(ae))
+        )
+      )
+    )
+  ),
+  log('js-fp3 done', 'Demo completed.')
+);
diff --git a/js-fp3/infrastructure/repository.js b/js-fp3/infrastructure/repository.js
new file mode 100644
index 0000000..0a26435
--- /dev/null
+++ b/js-fp3/infrastructure/repository.js
@@ -0,0 +1,69 @@
+import { ok, fail } from '../library/result.js';
+import { logReturn } from '../library/logging.js';
+import { accountNotFound } from '../domain/account.js';
+
+/**
+ * @typedef {Object} Repository
+ * @property {(id: string) => import('../library/result.js').Result<import('../domain/account.js').Account, import('../domain/account.js').AccountError>} loadAccount
+ * @property {(account: import('../domain/account.js').Account) => import('../library/result.js').Result<import('../domain/account.js').Account, import('../domain/account.js').AccountError>} saveAccount
+ */
+
+/** @typedef {{ type: 'RepositoryCreationFailed', message: string }} AppErrorRepositoryCreationFailed */
+/** @typedef {{ type: 'InnerAccountError', innerError: import('../domain/account.js').AccountError }} AppErrorInnerAccountError */
+
+/** @typedef {AppErrorRepositoryCreationFailed | AppErrorInnerAccountError} AppError */
+
+/**
+ * @param {string} message
+ * @returns {AppErrorRepositoryCreationFailed}
+ */
+export const repositoryCreationFailed = (message) => ({
+  type: 'RepositoryCreationFailed',
+  message,
+});
+
+/**
+ * @param {import('../domain/account.js').AccountError} innerError
+ * @returns {AppErrorInnerAccountError}
+ */
+export const innerAccountError = (innerError) => ({
+  type: 'InnerAccountError',
+  innerError,
+});
+
+/**
+ * @returns {Repository}
+ */
+export const createInMemoryRepository = () => {
+  /** @type {Map<string, import('../domain/account.js').Account>} */
+  const store = new Map();
+
+  /**
+   * @param {string} id
+   * @returns {import('../library/result.js').Result<import('../domain/account.js').Account, import('../domain/account.js').AccountError>}
+   */
+  const getById = (id) =>
+    store.has(id)
+      ? logReturn(
+          `[Repo] Loaded account ${id}`,
+          ok(store.get(id))
+        )
+      : logReturn(
+          `[Repo] Account ${id} not found`,
+          fail(accountNotFound(id))
+        );
+
+  /**
+   * @param {import('../domain/account.js').Account} account
+   * @returns {import('../library/result.js').Result<import('../domain/account.js').Account, import('../domain/account.js').AccountError>}
+   */
+  const save = (account) => {
+    store.set(account.id, account);
+    return logReturn(
+      `[Repo] Saved account ${account.id} with balance ${account.balance.amount.toFixed(2)}`,
+      ok(account)
+    );
+  };
+
+  return { loadAccount: getById, saveAccount: save };
+};
diff --git a/js-fp3/library/logging.js b/js-fp3/library/logging.js
new file mode 100644
index 0000000..f54496e
--- /dev/null
+++ b/js-fp3/library/logging.js
@@ -0,0 +1,59 @@
+import { tap, tapError } from './result.js';
+
+/**
+ * @template T
+ * @param {string} message
+ * @param {T} r
+ * @returns {T}
+ */
+export const logReturn = (message, r) => {
+  console.log(message);
+  return r;
+};
+
+/**
+ * @template T
+ * @param {string} src
+ * @param {string} message
+ * @returns {(x: T) => void}
+ */
+export const output = (src, message) => (x) => {
+  const value = typeof x === 'object' ? JSON.stringify(x) : x;
+  console.log(`[${src}] ${message} | ${value}`);
+};
+
+/**
+ * @template T
+ * @param {string} src
+ * @param {(x: T) => string} renderText
+ * @returns {(x: T) => void}
+ */
+export const outputWith = (src, renderText) => (x) => {
+  console.log(`[${src}] ${renderText(x)}`);
+};
+
+/**
+ * @template E
+ * @param {string} src
+ * @param {E} error
+ */
+export const outputError = (src, error) => {
+  const value = typeof error === 'object' ? JSON.stringify(error) : error;
+  console.error(`\x1b[1;31m[${src} ERROR]\x1b[0m ${value}`);
+};
+
+/**
+ * @template T, E
+ * @param {string} src
+ * @param {string} message
+ * @returns {(result: import('./result.js').Result<T, E>) => import('./result.js').Result<T, E>}
+ */
+export const log = (src, message) => tap(output(src, message));
+
+/**
+ * @template T, E
+ * @param {string} src
+ * @param {(x: T) => string} renderText
+ * @returns {(result: import('./result.js').Result<T, E>) => import('./result.js').Result<T, E>}
+ */
+export const logWith = (src, renderText) => tap(outputWith(src, renderText));
diff --git a/js-fp3/library/result.js b/js-fp3/library/result.js
new file mode 100644
index 0000000..a2b4a44
--- /dev/null
+++ b/js-fp3/library/result.js
@@ -0,0 +1,119 @@
+/**
+ * @template T, E
+ * @typedef {Object} Result
+ * @property {boolean} isSuccess
+ * @property {boolean} isFailure
+ * @property {T} [value] - Present when isSuccess is true
+ * @property {E} [error] - Present when isFailure is true
+ */
+
+/**
+ * @template T, E
+ * @param {T} value
+ * @returns {Result<T, E>}
+ */
+export const ok = (value) => ({
+  isSuccess: true,
+  isFailure: false,
+  value,
+});
+
+/**
+ * @template T, E
+ * @param {E} error
+ * @returns {Result<T, E>}
+ */
+export const fail = (error) => ({
+  isSuccess: false,
+  isFailure: true,
+  error,
+});
+
+/**
+ * @template T, E
+ * @param {() => T} f
+ * @param {(err: Error) => E} exceptionMapper
+ * @returns {Result<T, E>}
+ */
+export const catchResult = (f, exceptionMapper) => {
+  try {
+    return ok(f());
+  } catch (e) {
+    return fail(exceptionMapper(e));
+  }
+};
+
+/**
+ * @template TIn, TOut, E
+ * @param {(value: TIn) => Result<TOut, E>} binder
+ * @returns {(result: Result<TIn, E>) => Result<TOut, E>}
+ */
+export const bind = (binder) => (result) =>
+  result.isSuccess ? binder(result.value) : fail(result.error);
+
+/**
+ * @template TIn, TOut, E
+ * @param {(value: TIn) => TOut} mapper
+ * @returns {(result: Result<TIn, E>) => Result<TOut, E>}
+ */
+export const map = (mapper) => (result) =>
+  result.isSuccess ? ok(mapper(result.value)) : fail(result.error);
+
+/**
+ * @template T, E
+ * @param {(value: T) => void} action
+ * @returns {(result: Result<T, E>) => Result<T, E>}
+ */
+export const tap = (action) => (result) => {
+  if (result.isSuccess) action(result.value);
+  return result;
+};
+
+/**
+ * @template T, E
+ * @param {(error: E) => void} action
+ * @returns {(result: Result<T, E>) => Result<T, E>}
+ */
+export const tapError = (action) => (result) => {
+  if (result.isFailure) action(result.error);
+  return result;
+};
+
+/**
+ * @template T, EIn, EOut
+ * @param {(error: EIn) => EOut} mapper
+ * @returns {(result: Result<T, EIn>) => Result<T, EOut>}
+ */
+export const mapError = (mapper) => (result) =>
+  result.isSuccess ? ok(result.value) : fail(mapper(result.error));
+
+/**
+ * @template T, E, TResult
+ * @param {(value: T) => TResult} onSuccess
+ * @param {(error: E) => TResult} onFailure
+ * @returns {(result: Result<T, E>) => TResult}
+ */
+export const match = (onSuccess, onFailure) => (result) =>
+  result.isSuccess ? onSuccess(result.value) : onFailure(result.error);
+
+/**
+ * @template T, E
+ * @param {(value: T) => void} onSuccess
+ * @param {(error: E) => void} onFailure
+ * @returns {(result: Result<T, E>) => void}
+ */
+export const switch_ = (onSuccess, onFailure) => (result) => {
+  if (result.isSuccess) onSuccess(result.value);
+  else onFailure(result.error);
+};
+
+/**
+ * Pipe a result through a series of functions (left-to-right composition).
+ * This allows chaining without extending the prototype.
+ * @template T, E
+ * @param {Result<T, E>} result
+ * @param {...Function} fns
+ * @returns {Result<any, any>}
+ */
+export const pipe = (result, ...fns) =>
+  fns.reduce((acc, fn) => fn(acc), result);
diff --git a/js-fp3/package.json b/js-fp3/package.json
new file mode 100644
index 0000000..139587d
--- /dev/null
+++ b/js-fp3/package.json
@@ -0,0 +1,10 @@
+{
+  "name": "js-fp3",
+  "version": "1.0.0",
+  "description": "Functional DDD demo with intense FP patterns",
+  "type": "module",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js"
+  }
+}