# Palindrome Implementation - via JavaScript

## Introduction


- 
This is the 2nd post in the DS and Algo practice series.


- 
Here we would have a look at what is a palindrome and implement it via JavaScript.


## What is a Palindrome ?


- 
Well, palindrome is a string which when reversed generates the same string.


- 
For ex: **"abba"**, **"civic"**. If we reverse either **"abba"** or **"civic"**, we would get back the same string.

## Implementations

#### 1) We would reverse the input string and then compare the reversed string with the input one.
We ignore the spaces and case sensitivity, while looking for palindromes.

Ex: **"taco cat"** when reversed would ideally generate the same string when reversed. Here we need to ignore the white space while doing comparison. Same goes for case sensitivity.

```
//Palindrome
function isPalindrome(str) {
  if (!str) {
    return "Invalid Input";
  }
  let reversedStr = str
    .replace(/ +/g, "")
    .split("")
    .reduce((rev, item) => item + rev, "");

  return str.replace(/ +/g, "").toLowerCase() === reversedStr.toLowerCase();
}

console.log(isPalindrome("abba"));
console.log(isPalindrome("abcd"));
console.log(isPalindrome("racecar"));
console.log(isPalindrome("civic"));
console.log(isPalindrome("taco cat"));
console.log(isPalindrome("Aibohphobia"));
console.log(isPalindrome(null));
console.log(isPalindrome(""));
console.log(isPalindrome("A Santa Lived As a Devil At NASA"));
```

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1637821665775/OmBpXJrAa.png)

#### 2) Second implementation makes using of  [*Array.prototype.every()*](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every)  method of JavaScript, would be slightly lengthier option than the first one, because *every()* method will try to traverse every single element of the incoming array. 
But anyways, its an alternate implementation and it's always better to know multiple solutions to a problem.

```
//Alternate implementation using every() method
function isPalindromeUsingEvery(str) {
  if (!str) {
    return "Invalid Input";
  }
  let trimmedStr = str.replace(/ +/g, "");
  return trimmedStr.split("").every((item, index) => {
    return (
      item.toLowerCase() ===
      trimmedStr[trimmedStr.length - index - 1].toLowerCase()
    );
  });
}

console.log(isPalindromeUsingEvery("abba"));
console.log(isPalindromeUsingEvery("abcd"));
console.log(isPalindromeUsingEvery("racecar"));
console.log(isPalindromeUsingEvery("civic"));
console.log(isPalindromeUsingEvery("taco cat"));
console.log(isPalindromeUsingEvery("Aibohphobia"));
console.log(isPalindromeUsingEvery(null));
console.log(isPalindromeUsingEvery(""));
console.log(isPalindromeUsingEvery("A Santa Lived As a Devil At NASA"));
```

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1637822225031/sExbSWE6P.png)

## Github Link
Full code is present at - https://github.com/anurag1302/dsalgo-javascript/blob/main/practice/palindrome/index.js