const obj = {
  name: 'Calculator',
  values: [1, 2, 3, 4, 5],
  
  regular: function() {
    return this.values.filter(function(x) {
      return x > 2;
    }).length;
  },
  
  arrow: function() {
    return this.values.filter(x => x > 2).length;
  },
  
  broken: () => {
    return this.values.filter(x => x > 2).length;
  }
};

console.log(obj.regular());
console.log(obj.arrow());
try {
  console.log(obj.broken());
} catch(e) {
  console.log('Error');
}

const a = { value: 1 };
const b = Object.create(a);
b.value = 2;

console.log(b.value);
console.log(a.value);

const obj = {
  name: 'Taylor',
  greet() {
    return `Hello, ${this.name}!`;
  },
  delayedGreet() {
    setTimeout(function() {
      console.log(this.greet());
    }, 100);
  }
};

obj.delayedGreet();

async function processValues() {
  try {
    console.log('Start');
    const a = await Promise.resolve('First');
    console.log(a);
    const b = await Promise.reject('Error');
    console.log(b);
    return 'Done';
  } catch (err) {
    console.log(err);
    return 'Recovered';
  } finally {
    console.log('Finally');
  }
}

processValues().then(result => console.log(result));

const a = [1, 2, 3];
const b = a.slice(0, 2).push(4);
console.log(b);

function Person(name) {
  this.name = name;
  this.sayName = () => console.log(this.name);
}

const person1 = new Person('David');
const person2 = { name: 'Not David', sayName: person1.sayName };

person2.sayName();

function foo() {
   return typeof arguments;
};
console.log(foo(1, 2, 3));

let symbol1 = Symbol('denoscription');
let symbol2 = Symbol('denoscription');

const obj = {
  [symbol1]: 'value1',
  [symbol2]: 'value2'
};

console.log(obj[symbol1]);
console.log(symbol1 === symbol2);

class Calculator {
  static multiply(a, b) {
    return a * b;
  }
  
  static add = (a, b) => {
    return a + b;
  }
}

class ScientificCalculator extends Calculator {
  static multiply(a, b) {
    return super.multiply(a, b) * 2;
  }
}

console.log(Calculator.multiply(3, 4));
console.log(ScientificCalculator.add(5, 6));
console.log(ScientificCalculator.multiply(2, 3));

const obj = {
  value: 42,
  [Symbol.toPrimitive](hint) {
    if (hint === 'number') return this.value * 2;
    if (hint === 'string') return `Value: ${this.value}`;
    return this.value + 10;
  }
};

console.log(+obj);
console.log(`${obj}`);
console.log(obj + 5);
console.log(Number(obj));

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];

let columnSums = [];

for (let i = 0; i < matrix[0].length; i++) {
  let sum = 0;
  for (let j = 0; j < matrix.length; j++) {
    sum += matrix[i][i];
  }
  columnSums.push(sum);
}
console.log(columnSums);

function createCounter() {
  let count = 0;
  return {
    increment() {
      count++;
      return count;
    },
    getCount() {
      return count;
    }
  };
}

const counter = createCounter();

console.log(counter.increment());
console.log(counter.getCount());
console.log(counter.increment());
console.log(counter.getCount());

function* generator1() {
  yield 1;
  yield 2;
}

function* generator2() {
  yield* generator1();
  yield 3;
}

const gen = generator2();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);

class Logger {
  constructor(prefix) {
    this.prefix = prefix;
  }
  log(message) {
    console.log(`${this.prefix}: ${message}`);
  }
}

class Database {
  constructor(logger) {
    this.logger = logger;
  }
  save(data) {
    this.logger.log(`Saving ${data}`);
    return `${data}_saved`;
  }
}

const logger = new Logger('DB');
const db = new Database(logger);
const result = db.save('user');
console.log(result);

class LightMachine {
  constructor() {
    this.states = {
      green: { next: 'yellow' },
      yellow: { next: 'red' },
      red: { next: 'green' }
    };
    this.currentState = 'green';
  }

  transition() {
    this.currentState = this.states[this.currentState].next;
    return this.currentState;
  }
}

const lightMachine = new LightMachine();
let result = '';
for (let i = 0; i < 5; i++) {
  result += lightMachine.transition() + ' ';
}
console.log(result.trim());