Palindrome in JavaScript

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We will understand how to check whether a given value is a palindrome or not in JavaScript. A palindrome is a value that reads the same from backward or forward. To perform this check we will use the following approaches:

Approach 1:

Iterate over the string from forward and backward direction
Check if the character match
Return false for the first character that does not match
Return true if all the comparisons are performed and the characters match

Example: This example implements the above approach.

Javascript

function isPalindrome(str) { 
    var j = str.length-1 
    for(var i=0; i<str.length/2; i++){ 
        if(str[i]!=str[j]){ 
            return false; 
        } 
        j--; 
    } 
    return true; 
} 
  
var str1 = "racecar"; 
var str2 = "nitin"; 
var str3 = "Rama"; 
  
console.log(isPalindrome(str1)); 
console.log(isPalindrome(str2)); 
console.log(isPalindrome(str3));

Output:

true
true
false

Approach 2:

Initialize a variable and store the reverse of the value in it using for loop
Compare the original value with the reversed value
If both values are equal return true else return false

Example: This example implements the above approach.

Javascript

function isPalindrome(str) { 
    var rev=""; 
    for(var i=str.length-1; i>=0; i--){ 
        rev+= str[i]; 
    } 
    if(rev==str){ 
        return true
    } else{ 
        return false; 
    } 
} 
  
var str1 = "racecar"; 
var str2 = "nitin"; 
var str3 = "Rama"; 
  
console.log(isPalindrome(str1)); 
console.log(isPalindrome(str2)); 
console.log(isPalindrome(str3));

Output:

true
true
false

Approach 3:

Use inbuilt string methods like split() to split the string into characters array
Reverse the array using reverse() method
Join the array into a string using join() method
Store this value inside another variable
Compare the values and return true if both are equal

Example: This example implements the above approach on string

Javascript

function isPalindrome(str) { 
    var rev=str.split("").reverse().join(""); 
  
    if(rev == str){ 
        return true
    } 
    return false
                 
} 
  
var str1 = "racecar"; 
var str2 = "nitin"; 
var str3 = "Rama"; 
  
console.log(isPalindrome(str1)); 
console.log(isPalindrome(str2)); 
console.log(isPalindrome(str3));

Output:

true
true
false

Example: This example implements the above approach to Number

Javascript

function isPalindrome(num) { 
    var str = num.toString(); 
    var rev=str.split("").reverse().join(""); 
  
    if(rev == str){ 
        return true
    } 
    return false
                 
} 
  
var str1 = 1234321; 
var str2 = 112211; 
var str3 = 12345; 
  
console.log(isPalindrome(str1)); 
console.log(isPalindrome(str2)); 
console.log(isPalindrome(str3));

Output: The Number is first converted to a string and then compared using the previous approach

true
true
false

To know more about How to check whether a passed string is palindrome or not in JavaScript?

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