Performance · hard

39. BigInt precision for wei math

Avoid floating-point error in on-chain amounts.

Write `addWei(a, b)` accepting two wei amounts as strings, returning their sum as a string, using `BigInt` for exact precision.

Required in your answer: BigInt(

Transpiled, then run in a sandbox

function addWei(a, b) {
  // TODO
}

Output appears here.