let x = 5;

function foo() {
  console.log(x);
  let x = 10;
  console.log(x);
}

foo();

const team = {
  members: ['Alice', 'Bob', 'Charlie'],
  [Symbol.iterator]: function*() {
    let index = 0;
    while(index < this.members.length) {
      yield this.members[index++].toUpperCase();
    }
  }
};

const result = [];
for (const member of team) {
  result.push(member);
}

console.log(result.join('-'));

const obj = {};
let value = 0;

Object.defineProperty(obj, 'prop', {
  get() {
    return value;
  },
  set(newValue) {
    value = newValue + 1;
  },
  configurable: true,
  enumerable: true
});

obj.prop = 10;
console.log(obj.prop);

const a = async () => {
   return Promise.reject('rejected');
};

a().catch(error => console.log(error));
console.log('done');

const map = new WeakMap();

let obj1 = { name: 'user1' };
let obj2 = { name: 'user2' };

map.set(obj1, 'data for user1');
map.set(obj2, 'data for user2');

console.log(map.has(obj1));
obj1 = null;

console.log(map.has(obj1));
console.log(map.get(obj2));

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();

const user = {
  name: 'Sarah',
  age: 28,
  getName() {
    return this.name;
  }
};

const { getName } = user;
const boundGetName = user.getName.bind(user);

console.log(getName());
console.log(boundGetName());
console.log(user.getName());

function* outer() {
  yield 1;
  yield* inner();
  yield 4;
}

function* inner() {
  yield 2;
  yield 3;
}

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

function* counter() {
  let i = 1;
  while (true) {
    const reset = yield i++;
    if (reset) {
      i = 1;
    }
  }
}

const gen = counter();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next(true).value);
console.log(gen.next().value);

const config = { api: 'v1', timeout: 5000 };
Object.seal(config);

const settings = { theme: 'dark', lang: 'en' };
Object.freeze(settings);

config.api = 'v2';
config.retries = 3;
settings.theme = 'light';
settings.debug = true;

console.log(config.api);
console.log(config.retries);
console.log(settings.theme);
console.log(settings.debug);

const map = new Map();
const key1 = {};
const key2 = key1;

map.set(key1, "Value for key1");
map.set(key2, "Value for key2");

console.log(map.get(key2));
console.log(map.get(key1));