Why is my reverse() method not working ? Javascript palindrome problem

Question

This is the problem I'm trying to solve:

Write a Javascript code that checks whether a passed string is palindrome or not? Note: A palindrome is a word or phrase that reads the same backward as forward; eg. madam,racecar, etc.

And this is my code for it.. I'm not sure why it's not working. Can anyone assist?

function is_Palindrome (str){
  
   array1 = str.split('')
  array1_orig = array1.map(a => a)
  array2 = array1.reverse()
  console.log(array1_orig)
 console.log(array2)
  
  

  for (let i = 0; i <array1.length; i++){
    if(array1[i] === array2[i]){
      console.log("a match") 
    }
    else{
      console.log("not a match")
    }
  }


 

}


is_Palindrome("desk")

is_Palindrome("desk")

desk is obviously NOT a palindrome, so it should return "not a match" but the code isn't doing that

Best to use [...str] instead of split. Test both with "foo bar mañana mañana" — QuentinUK, May 19 '20 at 00:24

score 1 · Answer 1 · answered May 19 '20 at 12:39

In the line array1.reverse(), reverse will mutate the array1 object itself. This is cause of your issue.

Actually, you may not need to reverse call itself. You can just traverse the elements only till mid point and compare the ith element from start and end.

function is_Palindrome(str) {
  array1 = str.split("");

  const len = array1.length;
  let isMatch = true;

  for (let i = 0; i < len / 2; i++) {
    if (array1[i] !== array1[len - 1 - i]) {
      isMatch = false;
    }
  }
  return isMatch;
}

console.log("desk - ",is_Palindrome("desk"));
console.log("racecar - ", is_Palindrome("racecar"));

Thanks for the explanation! – Devenator May 23 '20 at 17:41 — Devenator, May 23 '20 at 17:41

score 0 · Answer 2 · answered May 19 '20 at 00:24

When calling myArray.reverse(), myArray gets reversed too.

I fixed the problem by using array1_orig instead :

function is_Palindrome (str){
  
   array1 = str.split('')
  array1_orig = array1.map(a => a)

  // Here, you are reversing array1 and storing the result in BOTH array1 and array2.
  array2 = array1.reverse()
  console.log(array1_orig)
 console.log(array2)
  
  

  for (let i = 0; i <array1_orig.length; i++){
    // Change both the line ABOVE and the line BELOW
    if(array1_orig[i] === array2[i]){
      console.log("a match") 
    }
    else{
      console.log("not a match")
    }
  }


 

}

console.log("Testing : DESK")
is_Palindrome("desk")
console.log("Testing : RACECAR")
is_Palindrome("racecar")

Thanks for the explanation! – Devenator May 23 '20 at 17:42 — Devenator, May 23 '20 at 17:42

Why is my reverse() method not working ? Javascript palindrome problem

2 Answers2