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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.

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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).

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