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);

var arr3=[1,2,3];
var pow1=arr3.map(x=>Math.pow(x,1));
var pow2=arr3.map(x=>Math.pow(x,2));
console.log(pow1);                  
console.log(pow2);

var str="good wood food cat bat hat";
console.log( str.match(/((g|w|f)ood)|((c|b|h)at)/g) );

function verify(username){
  return /^[a-z]\w{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 mysteriousFunction(a) {
  let result = 0;
  for (let i = 1; i <= a; i++) {
    if (i % 3 === 0 && i % 5 === 0) {
      result += i * 2;
    } else if (i % 3 === 0) {
      result += i;
    } else if (i % 5 === 0) {
      result -= i;
    }
  }
  return result;
}

console.log(mysteriousFunction(15));

var s="aaaabbbb";
console.log( s.match(/a+b/)+"" ); 
console.log( s.match(/a+b+/)+"" ); 
console.log( s.match(/ab+/)+"" ); 
console.log( s.match(/x+b+/)+"" );

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());