Add binary [https://leetcode.com/problems/add-binary]

add_binary.js

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
 var addBinary = function(a, b) {
     console.log(BigInt("0b"+a, 2) + BigInt("0b"+b, 2));

    // align strings
    if (a.length !== b.length) {
        a.length > b.length 
            ? b = '0'.repeat(a.length - b.length) + b 
            : a = '0'.repeat(b.length - a.length) + a;
    }
 
    const sumMap = new Map();
    sumMap.set('00', 0);
    sumMap.set('01', 1);
    sumMap.set('10', 1);
    sumMap.set('11', 10);

    let rest = 0;
    const result = [];
 
    for (let i = a.length - 1; i >= 0; i--) {
        let digit1 = a[i];
        let digit2 = b[i];

        if (rest) {
            digit1 = sumMap.get(`${rest}${digit1}`);
            rest = 0;

            if (digit1 === 10) {
                digit1 = 0;
                rest = 1;
            }
        }

        const sumResult = sumMap.get(`${digit1}${digit2}`);

        if (sumResult == 10) {
            result.push(0);
            rest = 1;

            continue;
        }

        result.push(sumResult);
    }

    if (rest) {
        result.push(1);
    }

    return result.reverse().join('');
};