jbmilgrom

class BankAccount {
  private balance;

  constructor(funds) {
    this.balance = funds;
  }

  public withdraw(amount) {
    this.balance = this.balance - amount; // <-- assign `this.balance` a new value
  }

jbmilgrom

const square = x => x * x;
const sum = (x, y) => x + y;

const sumOfSquares = (...nums) => nums.reduce((total, num) => sum(total, square(num)), 0);

sumOfSquares(1, 2, 3); // 14

jbmilgrom

const factorial = n => {
  let total = 1;
  while (n > 0) {
      total = total * n;
      n = n - 1;
  }
  return total;
};

factorial(0); // => 1

jbmilgrom

const factorial = n => {
  const iterate = (total, i) => {
    if (i === 0) return total;
    return iterate(total * i, i - 1);
  }
  return iterate(1, n);
};

factorial(0); // => 1
factorial(1); // => 1

jbmilgrom

let bankAccount = 100;

bankAccount = bankAccount - 20;

bankAccount; // 80

jbmilgrom

const makeBankAccount = balance => ({
  withdraw: amount => balance = balance - amount,  // <-- assign `balance` a new value
  checkBalance: () => balance
});

const bankAccount = makeBankAccount(100);
bankAccount.withdraw(20);
bankAccount.checkBalance(); // 80

jbmilgrom

const bankAccount = new BankAccount(100);

bankAccount.checkBalance(); // 100

bankAccount.withdraw(20);

bankAccount.checkBalance(); // 80

jbmilgrom

const space = (w1, w2) => `${w1} ${w2}`;
const sentence = words => `${words.reduce(space)}.`;

sentence(['i', 'heart', 'functions']); // => "i heart functions."

jbmilgrom

/**
 * With two _objects_, check equality by checking whether they are in fact the same object i.e. the reference.
 */
const areAccountsEqual = (a: BankAccount, b: BankAccount) => a === b;

const elainesAccount = new BankAccount(100);
const georgesAccount = new BankAccount(100);

elainesAccount.checkBalance(); // 100
georgesAccount.checkBalance(); // 100

jbmilgrom

const factorial = n => {
  if (n === 0) return 1;
  return n * factorial(n - 1);
};

factorial(1); // => 1
factorial(2); // => 2
factorial(3); // => 6