function aAn(word){
  return (/^[aeiou]/i.test(word) ? "An " : "A ") + word;
}
console.log( aAn("apple")) 
console.log( aAn("Apple"))  
console.log( aAn("egg"))   
console.log( aAn("car"))

function tricky() {
  let a = 1;
  let b = 2;
  const result = (function(a) {
    a = 3;
    return a + b;
  })(a);
  return result;
}

console.log(tricky());

var str="good wood food foot green glass roof";
var reg=/(.)\1/g
console.log( str.match(reg))  

let symbol1 = Symbol('description');
let symbol2 = Symbol('description');

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

console.log(obj[symbol1]);
console.log(symbol1 === symbol2);

var s="100001,111,12222221,222,3333,12321,14441";

var match1=s.match(/1.*1/g)
var match2=s.match(/1.+1/g)

console.log(match1)  
console.log(match2)

var str="a1!b2@c3#d4$e5%";
console.log( str.replace(/[^a-z]/g,""))  
console.log( str.replace(/[^0-9]/g,""))  
console.log( str.replace(/[^!@#$%]/g,""))

const wm = new WeakMap();
const obj1 = {};
const obj2 = {};
wm.set(obj1, 'object 1');
wm.set(obj2, 'object 2');
wm.delete(obj1);
console.log(wm.has(obj1));

var reg2=/^a..$/     
console.log(reg2.test("abc"))   
console.log(reg2.test("bbc"))   
console.log(reg2.test("abcd"))

var str="javascript coffeescript vbscript javacode"
var re1=/\b\w+script\b/g
var re2=/(?=java)\b\w+script\b/g
var re3=/(?!java)\b\w+script\b/g
console.log( str.match(re1))  
console.log( str.match(re2))  
console.log( str.match(re3))

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

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

console.log(result);

var str="dog,cat,pig,cow"
var re1=/\b\w+\b/g
var re2=/\b\w+\b(?=,cat|,pig)/g   
var re3=/\b\w+\b(?!,cat|,pig)/g
var re4=/(?=c)\b\w+\b(?!,cat|,pig)/g  
console.log( str.match(re1))  
console.log( str.match(re2))  
console.log( str.match(re3))  
console.log( str.match(re4)) 

const person = {
  name: 'Alice',
  age: 25,
  city: 'Wonderland'
};

const additionalInfo = {
  age: 30,
  occupation: 'Explorer'
};

const combined = {
  ...person,
  ...additionalInfo
};

console.log(combined.age);

var str="abba baab green glass roof";
var reg=/(.)(.)\2\1/g
console.log( str.match(reg))

❓Что будет на выходе?

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

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

❓Что будет на выходе?

function example() {
  console.log(a);
  var a = 10;
  console.log(a);
}
example();

❓Что будет на выходе?

var str="aaaabbbb";
console.log( str.match(/a{1}b{1}/)+"" );  
console.log( str.match(/a{2}b{2}/)+"" );  
console.log( str.match(/a{4}b{4}/)+"" ); 
console.log( str.match(/a{5}b{5}/)+"" );

function verify(username){
  return /^[a-z][a-z0-9_]{5,15}$/i.test(username);
}
console.log( verify("myjinxin2015"))  
console.log( verify("smile67"))       
console.log( verify("GiacomoSorbi"))  
console.log( verify("jhoffner"))      
console.log( verify("g964") )         
console.log( verify("matt c") )       /
console.log( verify("My_name_is_ZozoFouchtra") )

function addCommas(money){
  var re=/\d{3}/g
  return money.replace(re,x=>x+",")
}
console.log( addCommas("$123456789") )

function addCommas(money){
  var re=/\d{3}(?!$)/g
  return money.replace(re,x=>x+",")
}
console.log( addCommas("$123456789") )

const person = {
  firstName: 'John',
  lastName: 'Doe',
  age: 30,
  getFullName: function() {
    return this.firstName + ' ' + this.lastName;
  }
};

console.log(person.getFullName());

var str="javascript coffeescript vbscript javacode"
var re2=/(?=java)\b\w+script\b/g
console.log(str.match(re2))

var str="dog,cat,pig,cow"
var re2=/\b\w+\b(?=,cat|,pig)/g   
console.log(str.match(re2))