var word="abcd";
var regstr=word[0]+Array(word.length-1).join(".")+word.slice(-1);  
var reg3=new RegExp("^"+regstr+"$");
console.log(reg3)  

var words=["abc","123","&##"];
for (var r of words){
  var reg=new RegExp(r)
  console.log(reg)
}

var words=["abc","123","&##"];

const students = [
  { name: 'Alice', age: 20 },
  { name: 'Bob', age: 22 },
  { name: 'Charlie', age: 23 }
];

const studentToFind = { name: 'Bob', age: 22 };

const isIncluded = students.includes(studentToFind);

console.log(isIncluded);

var n=1.23456
var a=Math.round(n*100)/100
var b=Math.ceil(n*100)/100
var c=Math.floor(n*100)/100
console.log(a,b,c);

function isPair(s){
  var r=/\(\)|\[\]|\{\}/g;
  while (r.test(s)) s=s.replace(r,"");
  return s=="";
}
console.log( isPair(")()(") )   
console.log( isPair(")(") )    
console.log( isPair("({[})") )

var num=111.1234;
var s=num.toFixed(2)   //s=="111.12"
var a=parseInt(s),
    b=parseFloat(s),
    c= +s
console.log([a,b,c]) 

let arr = [1, 2, 3, 4, 5];
arr.length = 3;
arr.push(6, 7);
console.log(arr.length);

var str="  a b c  ";
console.log(str.trim());

let arr = [1, 2, 3, 4, 5];
arr.length = 3;
console.log(arr.length);
console.log(arr);

var str="Hello World!";
console.log(str.indexOf("world"))
console.log(str.lastIndexOf("world"))
console.log(str.search(/world/i))
console.log(str.search(/word/i))

var chars="abcde".split("");
for (var i=0;i<chars.length;i++){
  var tmp=chars[i].charCodeAt();
  if (tmp==97) console.log("a for apple");
  else console.log(tmp);
}

const person = {
  name: "Alice",
  age: 30,
  city: "New York"
};

const keys = Object.keys(person);
const values = Object.values(person);

const result = keys.map((key, index) => `${key}: ${values[index]}`);

console.log(result);

function plus(a,b,c,d,e){
  return a+b+c+d+e;
}
var arg1=[1,2,3,4,5];
var arg2=[2,3];
console.log(plus(...arg1));
console.log(plus(1,...arg2,4,5));

var str="abababab";
console.log( str.replace(/a/g, x=>x.toUpperCase()) );

var arr = Array.from({ length: 5 }, (v, i) => i * 2);
console.log(arr);

var a=[2,4,6,8]
var b=a.map((_,i,arr)=>arr[arr.length-1-i])
console.log(a)  
console.log(b) 

var a=1,b=2;
console.log(`${a} + ${b} = ${a+b}`);

function trickyCount(n) {
  if (n <= 1) return n;
  return trickyCount(n - 1) + trickyCount(n - 2);
}

function wrapCount(n) {
  return trickyCount(n) - trickyCount(n - 4);
}

console.log(wrapCount(6));

var arr=[[1,2],[3,4],[5,6]];
var result=[];
for (var i=0;i<arr.length;i++) 
  result=result.concat(arr[i]);
console.log(result);

var arr=['c','a','b'];
arr.sort();
console.log(arr)

function mystery(x) {
  return (function(y) {
    return x + y;
  })(x * 2);
}

const result1 = mystery(2);
const result2 = mystery(5);
const result3 = mystery(-1);

console.log(result1, result2, result3);