Binary addition in javascript

binary-addition.js

/**
 * Add two bits together and get resulting bits
 * 
 * @param {Number} a bit a 
 * @param {Number} b bit b
 * @returns {Array<Number, Number>} Carry and sum as a result of addition
 */
function addBits(a, b){
    return [ +( a && b ), +( a !== b ) ];
}

/**
 * Take two arrays of bits and add together
 * 
 * @param {Array<Number>} bitsA Array of bits
 * @param {Array<Number>} bitsB Array of bits
 * @returns {Array<Number>} Result adding bits
 */
function add(bitsA, bitsB){
    const bits = [];
    const length = Math.max( bitsA.length, bitsB.length );

    // Iterate from LSB
    for (let i = length - 1; i >= 0; i--) {
        const bitA = bitsA[i] || 0;
        const bitB = bitsB[i] || 0;

        const [carry, sum] = addBits(bitA, bitB);
        if (i === length - 1) {
            bits.unshift(carry, sum);
        } else {
            // Remove head (msb) and add to resulting sum
            const msb = bits.shift();
            bits.unshift(carry, sum + msb);
        }

    }
    return bits;
}


console.assert(
    addBits(1,1).join('') === '10'
);
console.assert(
    addBits(0,1).join('') === '01'
);
console.assert(
    addBits(1,0).join('') === '01'
);
console.assert(
    addBits(0,0).join('') === '00'
);
console.assert(
    add([0, 1, 0, 0, 0, 1, 1], [0, 1, 1, 0, 0, 1, 1]).join('') === '01010110'
);
console.assert(
    add([1, 1, 1, 1, 1, 1], [0, 0, 0, 0, 0, 0]).join('') === '0111111'
);
console.assert(
    add([1, 1, 1, 1, 1, 1], [1, 0, 0, 0, 0, 0]).join('') === '1011111'
);
console.assert(
    add([1], [1]).join('') === '10'
);