JavaScript Reverse the order of the bits in a given integer

We are required to write a JavaScript program that reverses the order of the bits in a given integer.

For example ?

56 -> 111000
after reverse 7 -> 111

Another example,

234 -> 11101010
after reverse 87 -> 1010111

How It Works

The algorithm converts the number to binary, reverses the binary string, and converts back to decimal:

1. Convert number to binary string using toString(2)
2. Split into array, reverse, and join back
3. Parse reversed binary string to decimal using parseInt(reversedBinary, 2)

Example

const num1 = 789;
const num = 43;

const reverseBits = (num = 1) => {
    const str = num.toString(2);
    const arr = str.split('').reverse();
    const arrStr = arr.join('');
    const reversedNum = parseInt(arrStr, 2);
    return reversedNum;
}

console.log("Original:", num, "-> Binary:", num.toString(2));
console.log("Reversed bits result:", reverseBits(num));
console.log();
console.log("Original:", num1, "-> Binary:", num1.toString(2));
console.log("Reversed bits result:", reverseBits(num1));

Original: 43 -> Binary: 101011
Reversed bits result: 53

Original: 789 -> Binary: 1100010101
Reversed bits result: 675

Step-by-Step Breakdown

const reverseBitsDetailed = (num) => {
    console.log("Input number:", num);
    
    const binary = num.toString(2);
    console.log("Binary representation:", binary);
    
    const reversed = binary.split('').reverse().join('');
    console.log("Reversed binary:", reversed);
    
    const result = parseInt(reversed, 2);
    console.log("Result as decimal:", result);
    
    return result;
}

reverseBitsDetailed(56);

Input number: 56
Binary representation: 111000
Reversed binary: 000111
Result as decimal: 7

Optimized Version

const reverseBitsOptimized = (num) => {
    return parseInt(num.toString(2).split('').reverse().join(''), 2);
}

// Test with multiple numbers
const testNumbers = [56, 234, 43, 789];
testNumbers.forEach(num => {
    console.log(`${num} -> ${reverseBitsOptimized(num)}`);
});

56 -> 7
234 -> 87
43 -> 53
789 -> 675

Conclusion

Reversing bits involves converting to binary, reversing the string, and parsing back to decimal. This technique is useful in algorithms requiring bit manipulation and cryptographic operations.