Let’s get practical

Exercise 1: Refactor to Classes

You are given the following code that manages a bank account using plain objects and functions:

function createAccount(owner, balance) {
  return { owner, balance, transactions: [] };
}

function deposit(account, amount) {
  if (amount <= 0) throw new Error("Deposit amount must be positive");
  account.balance += amount;
  account.transactions.push({ type: "deposit", amount, date: new Date().toISOString() });
}

function withdraw(account, amount) {
  if (amount <= 0) throw new Error("Withdrawal amount must be positive");
  if (amount > account.balance) throw new Error("Insufficient funds");
  account.balance -= amount;
  account.transactions.push({ type: "withdrawal", amount, date: new Date().toISOString() });
}

function getStatement(account) {
  return account.transactions
    .map(t => `${t.date} | ${t.type} | ${t.amount} | Balance: ${account.balance}`)
    .join("\\n");
}

// Usage
const acc = createAccount("Alice", 100);
deposit(acc, 50);
withdraw(acc, 30);
console.log(getStatement(acc));

Task

Convert the code above into a BankAccount class.
owner and balance should be set via the constructor. transactions is initialized as an empty array.
deposit(amount), withdraw(amount), and getStatement() become methods.
Make balance and transactions private using # private fields. Expose balance through a getter.
The usage code should work like this:

const alice = new BankAccount("Alice", 100);
const bob = new BankAccount("Bob", 50);
alice.deposit(200);
bob.withdraw(20);
console.log(alice.balance);        // 300
console.log(alice.getStatement());
console.log(bob.balance);          // 30
console.log(bob.getStatement());

Exercise 2: Task manager

Build a small task management system using two classes.

Class Task

Constructor takes title (string) and priority ("low", "medium", "high").
Has a boolean property done, initialized to false.
Has a method complete() that sets done to true.
Has a method toString() that returns a string like: [HIGH] Buy groceries (done) or [LOW] Read book (pending).

Class TaskManager

Maintains a private #tasks array.
add(title, priority) — creates a Task and adds it to the list. Returns the created task.
complete(title) — finds a task by title and marks it done. Throws an error if not found.
listPending() — returns an array of all tasks that are not done.
listByPriority(priority) — returns tasks filtered by the given priority.
summary() — returns an object: { total: 5, done: 2, pending: 3 }.

Exercise 3:

Exercise 4:

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Week 11 - OOP concepts & LLMs