console.log(Math.round(1.45)); 
console.log(Math.ceil(1.45));  
console.log(Math.floor(1.45));
console.log(Math.round(1.55)); 
console.log(Math.ceil(1.55));  
console.log(Math.floor(1.55));

var str="example";
var result=str.replace("e","@");
console.log(result);

'use strict';

function strictModeExample() {
  undeclaredVariable = 10;
  try {
    console.log(undeclaredVariable);
  } catch (e) {
    console.log('Error:', e.message);
  }
}

strictModeExample();

let obj = { a: 1 };
Object.freeze(obj);

console.log(Object.isFrozen(obj));
console.log(obj.a = 2);
console.log(obj.a);

var str="My".concat("name","is","John");
console.log(str);

function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
}

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

Что будет на выходе?

const arr = [];
arr.length = 3;
arr[2] = 1;
arr.forEach((el, i) => console.log(i))

const symbol1 = Symbol('symbol');
const symbol2 = Symbol('symbol');

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

console.log(obj[symbol1]);

function recursivePascalTriangle(n, row = [1], triangle = []) {
  triangle.push(row);
  if (n === triangle.length) {
    return triangle;
  }
  const nextRow = [1];
  for (let i = 1; i < row.length; i++) {
    nextRow.push(row[i] + row[i - 1]);
  }
  nextRow.push(1);
  return recursivePascalTriangle(n, nextRow, triangle);
}

const result = recursivePascalTriangle(5);

console.log(result);

var arr=[1,2,3,4,5];
console.log(arr.join());      
console.log(arr.join(","));   
console.log(arr.join(" "));   
console.log(arr.join("and"));

function outerFunction() {
  let x = 10;
  function innerFunction() {
    x += 5;
    console.log(x);
  }
  return innerFunction;
}

const closureFunc = outerFunction();
closureFunc();
closureFunc();

function rndnum(from,to){
  return ~~((to-from)*Math.random()+from);
}
for (var i=0;i<5;i++) console.log(rndnum(20,30));

var arr=[[9,0],[5,3],[2,6],[7,8]];
var result=[];
for (var i=0;i<arr.length;i++) 
  result=result.concat(arr[i]);
console.log(result);  

var arr=[[9,0],[5,3],[2,6],[7,8]];
var result=[];
for (var i=0;i<arr.length;i++) 
  result=result.concat(arr[i]);
console.log(result.sort()); 

const promise = new Promise((resolve, reject) => {
  reject('Error occurred');
});

promise
  .then(() => {
    console.log('Promise resolved!');
  })
  .catch(error => {
    console.log(error);
  })
  .then(() => {
    console.log('Process completed');
  });

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())]);