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;  }