BigNumber multiplying decimal values in ethers

Question

I want to do math - 100000 * 1.004 by using BigNumber values. The biggest problem here is that 1.004 is a float and BigNumber does not accept it. I am using ethers.js library for it.

I tried to use parseUnits("1.004", 18). I am using 18 because basically I am operating on stable coins prices.

I get BigNumber { value: "1004000000000000000" } from it. To do the math I have to parse 100000 also so I do it in the same way - parseUnits("100000", 18). After that I just do parseUnits("1.004", 18).mul(parseUnits("100000", 18)) to multiply them and I get BigNumber { value: "100400000000000000000000000000000000000000" }.

When I use formatUnits() method to get a number back I get 100400000000000000000000.0 where correct value should be 100000 * 1.004 = 100400.

What is the correct way of doing calculations like that by using the ethers.js library?

Answer 1

I finally decided to use bignumber.js library for that. ethers.js does not support float values with decimals when bignumber.js does it perfectly without any formatting.