js大整数相加

function sum(a, b) {
let len = Math.max(a.length, b.length)
a = a.padStart(len, '0')
b = b.padStart(len, '0')
let carry = 0
let result = ''
for (let i = len - 1; i >= 0; i--) {
const sum = +a[i] + +b[i] + carry
result = (sum % 10) + result
carry = Math.floor(sum / 10)
// if (sum > 9) {
// carry = 1
// } else {
// carry = 0
// }
}
if (carry) {
result = carry + result
}
return result
}