const obj1 = {
  a: 1,
  method() {
    return this.a;
  }
};

const obj2 = Object.create(obj1);
obj2.a = 777;

console.log(obj2.method());

function multiply(a, b) {
  if (b === 0) {
    return 0;
  } else if (b > 0) {
    return a + multiply(a, b - 1);
  } else {
    return -multiply(a, -b);
  }
}

console.log(multiply(300, 0));

let weakmap = new WeakMap();

let obj1 = {};
let obj2 = {};

weakmap.set(obj1, 'value1');
weakmap.set(obj2, 'value2');

obj1 = null;

console.log(weakmap.has(obj1));

function Person(name, age) {
  this.name = name;
  this.age = age;
}

Person.prototype.getDetails = function() {
  return this.name + ' is ' + this.age + ' years old.';
};

const john = new Person('John', 25);
console.log(john.getDetails());

var data=[1,2,3,4,5];
var filterData=a.filter(function(x){return x<=5});
console.log(filterData);

var names=["John","Tom","Jerry","Minne","Alice","othername..."];
for (var i=0;i<5;i++) 
  console.log(names[~~(names.length*Math.random())]);

const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const mergedObj = { ...obj1, ...obj2 };
console.log(mergedObj);

function removeOdd(arr){
  //remove odd number of arr
  for (var i=arr.length;i>=0;i--)
    if (arr[i]%2) arr.splice(i,1)
  return arr;
}
console.log(removeOdd([1,2,3,4,5]))   
console.log(removeOdd([1,3,5,7,9]))

let person = {
  name: 'Alice',
  age: 30,
  valueOf: function() {
    return this.age;
  }
};

let result = person + 10;
console.log(result);

var a=[1,2,3,4,5];
console.log(a.some(x=>x>4)); 
console.log(a.some(x=>x>5));

const numbers = [1, 2, 3, 4, 5];

const result = numbers
  .filter(num => num % 2 === 0)
  .map(num => num * num)
  .reduce((acc, num) => acc + num, 0);

console.log(result);

let x = { 
   a: 1,
   b: 2
};
let y = {
   b: 3,
   c: 4
};
Object.setPrototypeof(x, y);
console.log(x.b);

var arr1=[1,2,3,4,5]
arr1.reverse()
console.log(arr1)   
var arr2=['a','b','c']
arr2.reverse()
console.log(arr2)

const sym1 = Symbol('description');
const sym2 = Symbol('description');

const obj = {
  [sym1]: 'value1',
  [sym2]: 'value2'
};

console.log(obj[sym1]);

var x = 1;
function changeX() { x = 2; }
changeX();
console.log(x);

❓Что будет на выходе?

const array = [1, 2, 3, 4];
const result = array.reduceRight((acc, val) => acc - val);

console.log(result);

❓Что будет на выходе?

const weakMap = new WeakMap();
const array = [1, 2, 3];
const obj = {};

weakMap.set(obj, array);

const result = weakMap.get(obj).reduce((acc, val) => acc + val);

console.log(result);

function trickyScope() {
  var x = 10;
  if (true) {
    let x = 5;
    console.log(x);
  }
  console.log(x);
}

trickyScope();

const string = "JavaScript test";
const result = string.replace(/l/g, "");
console.log(result);

❓Что будет на выходе?

const obj = Object.freeze({
  a: [1, 2, 3],
  b: {
    c: 4
  }
});

obj.a.push(obj.b);
obj.b.c = 5;

console.log(obj.a);
console.log(obj.b.c);

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);