Binary array to corresponding decimal in JavaScript

Problem

We are required to write a JavaScript function that takes in a binary array (consisting of only 0 and 1).

Our function should first join all the bits in the array and then return the decimal number corresponding to that binary.

Method 1: Using Math.pow() with Manual Calculation

This approach calculates the decimal value by iterating through the array and using powers of 2:

const arr = [1, 0, 1, 1];
const binaryArrayToNumber = arr => {
    let num = 0;
    for (let i = 0, exponent = arr.length - 1; i < arr.length; i++) {
        if (arr[i]) {
            num += Math.pow(2, exponent);
        }
        exponent--;
    }
    return num;
};
console.log(binaryArrayToNumber(arr));

11

Method 2: Using parseInt() with join()

A simpler approach is to join the array elements into a string and use parseInt() with base 2:

const arr = [1, 0, 1, 1];
const binaryArrayToNumber = arr => {
    return parseInt(arr.join(''), 2);
};
console.log(binaryArrayToNumber(arr));

11

Method 3: Using reduce() with Bit Shifting

This method uses the reduce function with left bit shifting for efficient calculation:

const arr = [1, 0, 1, 1];
const binaryArrayToNumber = arr => {
    return arr.reduce((acc, bit) => (acc << 1) + bit, 0);
};
console.log(binaryArrayToNumber(arr));

11

How It Works

For the binary array [1, 0, 1, 1], the decimal conversion works as follows:

• Position 3 (leftmost): 1 × 2³ = 8
• Position 2: 0 × 2² = 0
• Position 1: 1 × 2¹ = 2
• Position 0 (rightmost): 1 × 2? = 1
• Total: 8 + 0 + 2 + 1 = 11

Comparison

Conclusion

The parseInt(arr.join(''), 2) method is the most straightforward approach for converting binary arrays to decimal. For performance-critical applications, consider using the bit shifting method with reduce().