How to reverse a number in JavaScript

In this post, you will learn how to reverse a number in JavaScript. Such a type of question can improve your logical problem solving skills. The interviewer can ask you to reverse a number in JavaScript with some particular approach. Here, we have mentioned how to reverse a number in JavaScript using different approaches.

In-built methods to reverse a number

Here, we have used the function toString(), split(), reverse(), and join() methods to reverse a number. The toString() converts a given number into a string. The split() method divides a string into an ordered list of substrings, places them in an array, and returns the array. The reverse() method changes the sequence of elements of the given array and returns the reverse sequence, and the join() method returns the array as a string. The Math.sign(num) multiplies the number with the sign of the original number provided, and the parseFloat(num) converts num into a float from a string.

// program to reverse a number
function reversedNumber(num) {
  return (
    parseFloat(
      num
        .toString()
        .split('')
        .reverse()
        .join('')
    ) * Math.sign(num)
  )                 
}

num = 34122332;
document.write("Original number: "+num+"<br/>");

result = reversedNumber(num);
document.write("Reverse number: "+result+"<br/>");

Original number: 34122332
Reverse number: 23322143

Reverse a number using while loop

Here, we are using a while loop to reverse a number. In this, we have passed the number to the reversedNumber() function and created a variable 'temp' and initialised it to 0. The while loop runs until the value of num is greater than 0. Inside the loop, we are getting the last number and adding it to temp as the last number. So that, we can get the reverse of the number.

// program to reverse a number
function reversedNumber(num) 
{

var a,b,temp=0;
b=num; 

while(num>0)
{
	a=num%10;
	num=parseInt(num/10);
	temp=temp*10+a;
} 
document.write("Reverse number: "+temp+"<br/>");
}

num = 34122332;
document.write("Original number: "+num+"<br/>");
reversedNumber(num);

Original number: 34122332
Reverse number: 23322143

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