Let's say that Ethereum solidity returns a number from one of its functions and I get that into Javascript.

Now ,because I write tests in my js application, I have to check if the returned value is equal to some number multiplied by some number.

Basically, let's look at the scenario.

In javascript,

Way 1)

web3.utils.toBN('100000000000000') * 30

Way 2)

web3.utils.toBN('100000000000000') * web3.utils.toBN('30')

Depending on the above 2 ones, can I use Way 1 ) ? reason is that if I use Way 2, my code just becomes bloated with toBN functions all the way.

1 Answer 1


Neither. You cannot use * to multiply two BNs together. For that you should use the mul function (https://github.com/indutny/bn.js/#arithmetics)

If what you are actually wanting to do is convert from/to wei/ether you can use web3.utils.toWei and web3.utils.toEther in combination with web3.utils.toBN, e.g., web3.utils.toBN(web3.utils.toWei("30", "ether")).

Note that you can use JavaScript's native BigInt for many calculations and comparisons. BigInt("0x100000000000000") * 30n is valid JavaScript and will produce a valid BigInt. You'll just need to ensure your target platforms support it (https://caniuse.com/?search=bigint).


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.