Javascript: How to Reverse an Integer

Last updated on June 23, 2022 The Plumber Loading... Post a comment

In Javascript, you can reverse a given integer (e.g. turn 123 to 321, -456 to -654, 1200 to 21) by performing the following steps:

  1. Convert the integer to a string
  2. Reverse that string
  3. Turn the reversed string to an integer. If the input is a negative number, we must multiply the result with -1 (because the minus sign will be lost even if the input is a negative integer)

These words might sound boring and unclear enough. The program below will help you understand the solution better:

function reverseInt(input){
     // turn the input to a string
     var str = input.toString();
     // reverse the string
     var reversedStr = str.split('').reverse().join('');

     // turn the reversed string to an integer
     var reversedInt = parseInt(reversedStr);

     // deal with the negative sign if it exists
     if('-') !== -1){
         reversedInt = reversedInt * -1;
     // return the result
     return reversedInt;

// Test it



We can condense the reverseInt() function above to make it more succinct like this:

function reverseInt(input) {
      return parseInt(input.toString().split('').reverse().join(''))
                * Math.sign(input);

That’s if. Further reading:

You can also check out our Javascript category page, TypeScript category page, Node.js category page, and React category page for the latest tutorials and examples.

Notify of
Inline Feedbacks
View all comments

You May Also Like