Reverse a Number - JavaScript Program

// Method 1: Using while loop function reverseNumber(num) { let reversed = 0; let original = num; while (num > 0) { let digit = num % 10; reversed = reversed * 10 + digit; num = Math.floor(num / 10); } return reversed; } console.log("Reverse of 1234:", reverseNumber(1234)); console.log("Reverse of 5678:", reverseNumber(5678)); // Method 2: Using string conversion function reverseNumberString(num) { return parseInt(num.toString().split('').reverse().join('')); } console.log("\nUsing string method:"); console.log("Reverse of 1234:", reverseNumberString(1234)); console.log("Reverse of 9876:", reverseNumberString(9876)); // Method 3: Using array methods function reverseNumberArray(num) { return parseInt( num.toString() .split('') .reverse() .join('') ); } console.log("\nUsing array methods:"); console.log("Reverse of 5432:", reverseNumberArray(5432)); // Method 4: Handling negative numbers function reverseNumberComplete(num) { let isNegative = num < 0; num = Math.abs(num); let reversed = 0; while (num > 0) { reversed = reversed * 10 + (num % 10); num = Math.floor(num / 10); } return isNegative ? -reversed : reversed; } console.log("\nWith negative support:"); console.log("Reverse of -1234:", reverseNumberComplete(-1234)); console.log("Reverse of 5678:", reverseNumberComplete(5678));

Reverse of 1234: 4321 Reverse of 5678: 8765 Using string method: Reverse of 1234: 4321 Reverse of 9876: 6789 Using array methods: Reverse of 5432: 2345 With negative support: Reverse of -1234: -4321 Reverse of 5678: 8765

This program demonstrates different methods to reverse a number.

Method 1: Mathematical Approach

Using modulo and division:

javascript
while (num > 0) {
    let digit = num % 10;        // Get last digit
    reversed = reversed * 10 + digit;  // Add to reversed
    num = Math.floor(num / 10);   // Remove last digit
}

How it works:

Extract last digit: num % 10
Add to reversed: reversed * 10 + digit
Remove last digit: Math.floor(num / 10)

Example: 1234

Iteration 1: digit=4, reversed=4, num=123
Iteration 2: digit=3, reversed=43, num=12
Iteration 3: digit=2, reversed=432, num=1
Iteration 4: digit=1, reversed=4321, num=0

Method 2: String Conversion

Convert to string, reverse, convert back:

javascript
num.toString().split('').reverse().join('')

String Methods:

toString(): Number to string
split(''): String to array
reverse(): Reverse array
join(''): Array to string
parseInt(): String to number

Method 3: Array Methods

Same as Method 2, more explicit:

javascript
num.toString()
   .split('')
   .reverse()
   .join('')

Method 4: Negative Number Support

Handle negative numbers:

javascript
let isNegative = num < 0;
num = Math.abs(num);  // Make positive
// ... reverse logic ...
return isNegative ? -reversed : reversed;

Math Methods:

Math.abs(): Absolute value
Math.floor(): Round down

When to Use:

Mathematical: Learning, efficient
String: Simple, readable
Array: Functional style

Output