Reverse a string by using three default or built-in functions:

function reverseStr(str) {    // str = "world";        // step 1: split the string by using of String.prototype.split()    let splitStr = str.split("");     /*      splitStr = str.split("");      ["w", "o", "r", "l","d"]    */        //step 2: reverse the new created array by String.prototype.reverse()    let reverseArr = splitStr.reverse();    /*      reverseArr = splitStr.reverse();      ["d", "l", "r", "o","w"]    */        //step 3: join the reverseArr by the using of String.prototype.join()    let joinStr = reverseArr.join("");    /*      joinStr = reverseArr.join("");      "dlrow"    */        return joinStr;  }

Perform a binary search within an array

function binary_Search(items, value){ var firstIndex = 0, lastIndex = items.length - 1, middleIndex = Math.floor((lastIndex + firstIndex)/2); while(items[middleIndex] != value && firstIndex < lastIndex) { if (value < items[middleIndex]) { lastIndex = middleIndex - 1; } else if (value > items[middleIndex]) { firstIndex = middleIndex + 1; } middleIndex = Math.floor((lastIndex + firstIndex)/2); } return (items[middleIndex] != value) ? -1 : middleIndex; } var items = [1, 2, 3, 4, 5, 7, 8, 9]; console.log(binary_Search(items, 1)); console.log(binary_Search(items, 5));  

Find the leap years from a given range of years

function leap_year_range(st_year, end_year) {
        var year_range = [];
        for (var i = st_year; i <= end_year; i++)
        {
             year_range.push(i);
        }
        var new_array = [];

  year_range.forEach(
   function(year)
    {
       if (test_LeapYear(year))
       new_array.push(year);
    });

  return new_array;
     }

function test_LeapYear(year) {
   if ((year % 4 === 0 && year % 100 !== 0) || (year % 100 === 0 && year % 400 === 0)) {
                return year;
        } else {
                return false;
        }
}

console.log(leap_year_range(2000,2012));