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nodejs-test

Test task for Node jS developers. Candidate should write a simple NPM package banking application in Typescript language.

General acceptance criteria

  • All code is in git repo (candidate can use his/her own github account).
  • Package name can be derived from ExBanking
  • Package simply exports just an initializer of the ExBanking module (no API endpoint, no REST / SOAP API, no TCP / UDP sockets, no any external network interface).
  • Application should not use any database / disc storage. All needed data should be stored only in application memory.
  • Candidate can use any Node library he/she wants to, the code itself should be written using Typescript and transpiled to Javascript.
  • We expect unit tests.
  • Code accuracy also matters. Readable, safe, refactorable code is a plus.

Money amounts

  • Money amount of any currency should not be negative.
  • Application should provide 2 decimal precision of money amount for any currency.
  • Amount of money incoming to the system should be equal to amount of money inside the system + amount of withdraws (money should not appear or disappear accidentally).
  • User and currency type is any string. Case sensitive. New currencies / users can be added dynamically in runtime. In the application, there should be a special public function (described below) for creating users. Currencies should be created automatically (if needed).

API reference

Requirements for public functions provided by ExBanking package. Any function should return success result or error result. Success result is different for each function, error result is generic.

type BankingError = Error | 
  WrongArguments | 
  UserAlreadyExists | 
  UserDoesNotExist |
  NotEnoughMoney | 
  SenderDoesNotExist | 
  ReceiverDoesNotExist;

type Ok = { success: true };
const createUser = (username: string): Ok | BankingError => {};
  • Function creates new user in the system
  • New user has zero balance of any currency
const deposit = (username: string, amount: number, currency: string): (Ok & { newBalance: number } | BankingError) => {};
  • Increases user's balance in given currency by amount value
  • Returns newBalance of the user in given format
const withdraw = (username: string, amount: number, currency: string): (Ok & { newBalance: number } | BankingError) => {};
  • Decreases user's balance in given currency by amount value
  • Returns new_balance of the user in given format
const getBalance = (username: string, currency: string): (Ok & { balance: number } | BankingError) => {};
  • Returns balance of the user in given format
const send = (fromUsername: string, toUsername: string, amount: number, currency: string): (Ok & { fromUsernameBalance: number, toUsernameBalance: number } | BankingError) => {};
  • Decreases fromUsername's balance in given currency by amount value
  • Increases toUsername's balance in given currency by amount value
  • Returns balance of fromUser and toUser in given format