What is the standard solution in JavaScript for handling big numbers (BigNum)?

Update(2019-08-19): BigInt is now part of Firefox and Chrome; you no longer need a library:

const bigInt1 = 1111111111111111111111111111111n;
const bigInt2 = BigInt("1111111111111111111111111111111")
console.log((bigInt1 + bigInt2)+"")

Original answer:

If you need arbitrary-precision decimal numbers, use Javascript-bignum, as it is correct and fast.