function reverseString(str) {

str = str.split("").reverse().join("")

return str;

}

reverseString("hello");

function factorialize(num) {

    let  sum = num ;

    if(num == 0){

       return 1 ;

    }else{

       while(num > 1 ){

        sum *= (num-1) ;

        num -- ;

    }

    }

return sum;

}

factorialize(0);

function palindrome(str) {

  str = str.replace(/[^a-zA-Z\d]/g, "");

  return str.toLowerCase() == str

      .split("")

      .reverse()

      .join("")

      .toLowerCase();

}

palindrome("0_0 (: /-\ :) 0-0");

function findLongestWord(str) {

    str = str.split(" ");

    let len = str[0].length ;

    for(let i = 0 ; i < str.length ; i++){

        if(len <= str[i].length){

            len = str[i].length ;

        }

    }

    return len;

}

findLongestWord("The quick brown fox jumped over the lazy dog");

function titleCase(str) {

    str = str.split(" ");

    for(let i = 0 ; i < str.length ; i++){

        str[i] =str[i].substring(0, 1).toUpperCase() + str[i].substring(1).toLowerCase();

    }

    str = str.join(" ");

return str;

}

titleCase("sHoRt AnD sToUt");

function largestOfFour(arr) {

    let newArr = [] ;

    for(let i = 0 ; i < arr.length ; i ++){

        let max = arr[i][0];

        for(let j = 0 ; j < arr[i].length ; j++){

            if(max <= arr[i][j]){

                max = arr[i][j];

            }

        }

    newArr.push(max);

}

return newArr;

}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

function confirmEnding(str, target) {

// "Never give up and good luck will find you."

// -- Falcor

console.log(str,"|||",str.substring(str.length-target.length))

// return str.substring(str.length-target.length) == target;

return str.endsWith(target);

}

confirmEnding("Bastian", "n");

function repeat(str, num) {

// repeat after me

    if(num < 0){

        return ""

    }else{

        let newStr = "" ;

        for(let i = 0 ; i < num ; i++){

            newStr += str ;

        }

        return newStr;

    }

}

repeat("abc", 3);

function truncate(str, num) {

// Clear out that junk in your trunk

    if(str.length <= num ){

        return str;

    }else{

       if(num <=3 ){

           return str.substring(0,num)+"...";

       } else{

           return str.substring(0,num-3)+"...";

       }

    }

}

truncate("Peter Piper picked a peck of pickled peppers", 14);

function chunk(arr, size) {

// Break it up.

    var index = 0;

    var newArray = [];

    while(index < arr.length) {

        newArray.push(arr.slice(index, index += size));

    }

    return newArray;

}

chunk(["a", "b", "c", "d"], 2);

function slasher(arr, howMany) {

// it doesn't always pay to be first

return arr.slice(howMany);

}

slasher([1, 2, 3], 2);

function mutation(arr) {

    let first = arr[0].toLowerCase();

    let target = arr[1].toLowerCase().split("") ;

    for(let i = 0 ; i < target.length ; i++){

        if(first.indexOf(target[i]) < 0 ){

            return false ;

        }

    }

    return true ;

}

mutation(["zyxwvutsrqponmlkjihgfedcba", "qrstu"]);

function bouncer(arr) {

// Don't show a false ID to this bouncer.

return arr.filter(params => Boolean(params));

}

function isBad(params){

    var result = Boolean(params);

    return result;

}

bouncer([7, "ate", "", false, 9]);

function destroyer(arr) {

  var args = [];

  for(var i = 1; i < arguments.length; i++){    //将待摧毁的值放入一个数组中，赋值给变量args

    args.push(arguments[i]);

  }

  var newArr=arr.filter(function(item){    //两个数组去重；

    return args.indexOf(item) === -1;

  });

  return newArr;

}

destroyer([1, 2, 3, 1, 2, 3], 2, 3);

function where(arr, num) {

// Find my place in this sorted array.

arr.push(num);

arr = arr.sort(function(x,y){    //将num扔进arr中之后排序；

        return x-y;

       });

       console.log(arr);

return arr.indexOf(num);

}

where([3, 10, 5], 3);

function rot13(str) { // LBH QVQ VG!

    var newArr=[];

    for(var i=0;i<str.length;i++){

        var numbers=str.charCodeAt(i);    //使用charCodeAt()方法取得每个字符的Unicode值，并保存在变量numbers中；

        if(numbers<65||numbers>90){

            newArr.push(String.fromCharCode(numbers));

        }else if(numbers>77){

            newArr.push(String.fromCharCode(numbers-13));

        }else{

            newArr.push(String.fromCharCode(numbers+13));

        }

    }      //大写A-Z字母对应的Unicode值为65-90；通过判断，利用fromCharCode()将Unicode值又转换为字符；

    return newArr.join("");

}

// Change the inputs below to test

rot13("SERR PBQR PNZC");