console.log(typeof null);
console.log(typeof undefined);
console.log(typeof {});
console.log(typeof []);

const num = 10;
const str = num.toString().padStart(0, "9");
console.log(str);

function* counter() {
  let i = 0;
  while (true) {
    const direction = yield i;
    if (direction === 'up') i += 2;
    else if (direction === 'down') i -= 1;
    else i += 1;
  }
}

const count = counter();
console.log(count.next().value);
console.log(count.next('up').value);
console.log(count.next('down').value);
console.log(count.next().value);

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* genSequence() {
  const result = yield 'first';
  console.log(result);
  yield* [1, 2];
  return 'done';
}

const gen = genSequence();
let next = gen.next('ignored');
console.log(next.value);
next = gen.next('second');
next = gen.next();
console.log(next.value);
next = gen.next();
console.log(next);

function calc(num) {
   return num + 0.01 * '0';
}

typeof calc('hello');

function Animal(name) {
  this.name = name;
}

Animal.prototype.getName = function() {
  return this.name;
};

function Dog(name, breed) {
  Animal.call(this, name);
  this.breed = breed;
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

Dog.prototype.getName = function() {
  return `Dog called ${Animal.prototype.getName.call(this)}`;
};

const myDog = new Dog('Rex', 'German Shepherd');
console.log(myDog.getName());

function asyncQuiz() {
  return new Promise((resolve) => {
    setTimeout(() => resolve('World'), 100);
  });
}

async function runAsyncQuiz() {
  const result = await asyncQuiz();
  console.log(result);
}

console.log('World');
runAsyncQuiz();

async function asyncArrayOperations() {
  const array1 = [1, 2, 3];
  const array2 = [4, 5, 6];
  const array3 = [7, 8, 9];

  const result = await Promise.all([array1, array2, array3].map(async arr => {
    return await arr.filter(async (acc, num) => {
      return (await acc) + num;
    }, Promise.resolve(0));
  }));

  console.log(result);
}

asyncArrayOperations();

console.log(new RegExp({}).test("test"));
console.log(new RegExp({}).test("why?"));
console.log(new RegExp({}).test("cause"));

const obj = {
  value: 42,
  getValue() {
    return this.value;
  },
  getValueArrow: () => this.value,
  nested: {
    value: 100,
    getValue() {
      return this.value;
    }
  }
};

const extractedMethod = obj.getValue;
const boundMethod = obj.getValue.bind(obj);

console.log(obj.getValue() + ',' + obj.getValueArrow() + ',' + 
            obj.nested.getValue() + ',' + extractedMethod() + ',' + 
            boundMethod());

const target = { a: 1, b: 2 };
const handler = {
  get(obj, prop) {
    return prop === 'sum' ? obj.a + obj.b : Reflect.get(obj, prop);
  },
  set(obj, prop, value) {
    if (prop === 'a' && value < 0) {
      return false;
    }
    return Reflect.set(obj, prop, value);
  }
};

const proxy = new Proxy(target, handler);
proxy.a = -5;
proxy.b = 10;
console.log(`${proxy.a}, ${proxy.b}, ${proxy.sum}`);

const string = "Hello, World!";

const result = [...string.matchAll(/[HlWrd]/g)]
                 .map(match => match[0])
                 .reverse()
                 .join("");

console.log(result);

const obj = {
  value: 10,
  getValue() {
    return this.value;
  },
  getArrowValue: () => {
    return this.value;
  },
  getMixedValue() {
    const regular = function() { return this.value; };
    const arrow = () => this.value;
    
    return [regular(), arrow()];
  }
};

console.log(obj.getMixedValue());

function recursiveReverseString(str) {
  return str === "" ? str : recursiveReverseString(str.substr(1)) + str;
}

const result = recursiveReverseString("hello");

console.log(result);

const sym = Symbol('unique');
const obj = {
  [sym]: 'symbol value',
  a: 0,
  b: 2,
  c: 1
};

const keys = Object.keys(obj);
const symbols = Object.getOwnPropertySymbols(obj);

console.log(keys.length, symbols.length);

const obj = {
  value: 42,
  getValue() {
    return this.value;
  },
  getArrowValue: () => {
    return this.value;
  },
  getDelayedValue() {
    setTimeout(function() {
      console.log(this.value);
    }, 0);
  },
  getFixedDelayedValue() {
    setTimeout(() => {
      console.log(this.value);
    }, 0);
  }
};

obj.getDelayedValue();

const arr = [1, 2, 3];
const str = arr.join([4]);
console.log(typeof str);
console.log(str);

const target = { name: 'Alice' };

const handler = {
  get(obj, prop) {
    return prop in obj ? obj[prop].toUpperCase() : 'NOT_FOUND';
  },
  set(obj, prop, value) {
    if (typeof value !== 'string') {
      return false;
    }
    obj[prop] = value.trim();
    return true;
  }
};

const proxy = new Proxy(target, handler);
proxy.name = '  Bob  ';
proxy.age = 30;

console.log(`${proxy.name}-${proxy.age}-${proxy.job}`);