What's wrong with following code for string reverse in javascript?

Question

function stringReverse(str){
    return str.split('').reverse().join('');
}

In an interview, i was asked to reverse a string. I solved it by above code but my interviewer said this is a bad solution. Then i used loop but he was not happy.

function stringReverse(str){
    var a = str.split(''), b=[];
    for(var i=0;i<arr.length;i++){
       b.push(a[a.length-1-i]);
    }
    return b.join('');
}

Please add your comments.

Answer 1

May be interviewer wanted you to handle null, undefined or blank string

without this check your code might throw this exception

Cannot read property 'split' of undefined

use this :

if( str) {
str.split('').reverse().join('')
}

will evaluate to true if value is not:

• null
• undefined
• NaN
• empty string ("")
• 0
• false

OR more specifically :

if( str && (typeof str == 'string') ) {
   // do something
}

refer this SO post for more details.

Answer 2

There are two possible ways your interviewer might not have been happy with your answer.

1. From my experience, when an interviewer asks you to reverse a string, you shouldn't use the existing functions for it. You should implement it from scratch. In your case, a nice approach would be to use recursion to solve the problem. Look at this link!

2. Performance issues! Using the reverse function is not the fastest way to reverse a string. Check this out!

Hope this solved your questions :)

Answer 3

This article deals with unicode symbols in JavaScript: JavaScript has a Unicode problem · Mathias Bynens

The best solution to your problem uses the Array.from method which works in all browsers except from Internet Explorer (MDN has a polyfill for that).

Here is a solution based on the articles answer to reverse a string:

function strReverse(str) {
  //Only allow numbers and strings to pass, else return empty string
  if (typeof str != 'string' && typeof str != 'number') {
    return '';
  }
  //Return the reversed string
  return Array.from(str.toString()).reverse().join('');
}
//TESTS
console.log([
  strReverse(),
  strReverse(null),
  strReverse("null"),
  strReverse(true),
  strReverse("▼ ▼▲ ▼"),
  strReverse(1138),
  strReverse(''),
  strReverse('fff'),
]);

Answer 4

In ECMAScript 6, you can reverse string like as below

var string = "hello";
var str = [...string].reverse().join('');
console.log(str);

Answer 5

When I was in 10th standard, Our computer teacher always asks every student to write a code to check if the given string is palindrome or not.

Palindrome string is a string which is always same as its reverse ex: mom = mom

In an interview, if someone asked you to write a code to reverse a string. Then he wants to see your logical approach to solve the problem. Existing function in any programming language has also code which actually put a logical approach and solves the problem.

Reverse code in java

import java.util.*;

class Reverse
{
  public static void main(String args[])
{
   String original, reverse = "";
   Scanner in = new Scanner(System.in);
   System.out.println("Enter a string to get reverse");
   original = in.nextLine();
   int length = original.length();
   for ( int i = length - 1; i >= 0; i-- )
     reverse = reverse + original.charAt(i);
 }
}

Answer 6

String words[] = str.split("\\s");
    String rev = "";
    for (String w : words) {
        StringBuilder sb = new StringBuilder(w);
        sb.reverse();
        rev += sb.toString() + " ";
    }
    System.out.println("\n reverse string=" + rev);