Adding Big Numbers in Javascript (string types)

function reverse(val) {
	return val.split('').reverse().join('')
} 

function add(a, b) {
	var rBig, rSmall;
	if ( Number(a) < Number(b) )  {
		rBig = reverse(b);
		rSmall = reverse(a);
	} else {
		rBig = reverse(a);
		rSmall = reverse(b);
	}

	var carry = 0, digit = 0, total = '';

	for (var i = 0; i < rBig.length; i ++) {
		digit = Number(rBig[i]) + (Number(rSmall[i]) || 0) + carry;
		carry = (digit > 9) ? Math.floor(digit / 10) : 0;
		total = ( String(digit > 9 ? digit % 10 : digit) ).concat(total);
	}

	// handle last carry if any
	if (carry == 1) {
		total = ('1').concat(total);
	}
	// while first digits are '0' pop them off
	while (total[0] === '0') total = total.slice(1);
	return total;
}