const symbol1 = Symbol('desc1');
const symbol2 = Symbol('desc2');
const myObject = {};
myObject[symbol1] = 'Value1';
myObject[symbol2] = 'Value2';
let output = '';
for (let key in myObject) {
  output += myObject[key] + ' ';
}
output += Object.getOwnPropertySymbols(myObject).length;
console.log(output);

const getValue = (x) => {
  console.log(`Getting: ${x}`);
  return x;
};

const obj = { name: null };

const result = obj.name || getValue('default') && getValue('final');
console.log(`Result: ${result}`);

const array = [1, 2, 3, 4, 5];
const result = array.filter(n => n % 2).map(n => n * 2);

console.log(result);

function createCounter() {
  let count = 0;
  return function(increment = 1) {
    count += increment;
    return count;
  };
}

const counter1 = createCounter();
const counter2 = createCounter();

console.log(counter1());
console.log(counter1(5));
console.log(counter2(3));
console.log(counter1());
console.log(counter2());

Promise.resolve(1)
.then(r => Promise.reject(r))
.catch(console.log)
.then(() => console.log(2));

let obj1 = { name: 'Sarah' };
let obj2 = { name: 'Mike' };
let obj3 = { ref: obj1 };

obj1.circular = obj1;
obj2.partner = obj3;
obj3.partner = obj2;

let weakMap = new WeakMap();
weakMap.set(obj1, 'data1');
weakMap.set(obj2, 'data2');

obj1 = null;
obj2 = null;

console.log(weakMap.has(obj3.ref));
console.log(obj3.partner.name);

const arr = [1, 2, 3, 4, 5];
const result = arr
  .map(x => x * 2)
  .filter(x => x > 5)
  .reduce((acc, val) => {
    return acc + (val % 3 === 0 ? val : 0);
  }, 0);

console.log(result);

const a = document.createElement("a");
a.id = "test1";
a.href = "test2";
document.body.appendChild(a);
console.log(window.test1);

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 };

const target = { name: 'Sarah', age: 25 };

const handler = {
  get(obj, prop) {
    if (prop in obj) {
      return obj[prop];
    }
    return `Property '${prop}' not found`;
  },
  set(obj, prop, value) {
    obj[prop] = value.toString().toUpperCase();
    return true;
  }
};

const proxy = new Proxy(target, handler);
proxy.city = 'boston';
console.log(proxy.name);
console.log(proxy.city);
console.log(proxy.country);

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();