How to input the bignumber with etherjs

Question

This is my solidity codes, I am trying to compare the variables passed with different variables. Because float data type is not supported by solidity and function input is default tailed with 18 zeros, I use the timeAmount to multiply 10^18.

function setUriToUpdate(uint256 temperature) public {
    uint256 timesAmount = 10 ** 18;
    if (temperature < 10 * timesAmount) {
       uriToUpdate = METADATA_BELOW;
    } else if (temperature > 10 * timesAmount && temperature < 20 * timesAmount) {
       uriToUpdate = METADATA_AVERAGE;
    } else if (temperature >= 20 * timesAmount && temperature < 50 * timesAmount) {
       uriToUpdate = METADATA_ABOVE;
    }
}

When I write my unit test in js code, I don't know to pass a variable tailed with 18 zeros.

await nft.connect(deployer).setUriToUpdate(15 * 10 ** 18)

The error is:

Error: overflow [ See: https://links.ethers.org/v5-errors-NUMERIC_FAULT-overflow ] (fault="overflow", operation="BigNumber.from", value=15000000000000000000, code=NUMERIC_FAULT, version=bignumber/5.7.0)

Can anyone tell me how to pass big number to the function?

thanks in advance!

Answer 1

The reason why is failing is because of the result of 15 * 10 ** 18 is beyond what is considered a safe range in Javascript.

If you print the result of this in Javascript:

console.log("Number.MAX_SAFE_INTEGER: ", Number.MAX_SAFE_INTEGER);

You'll get:

9007199254740991

Which is a 53-bit number. It has 16 digits.

If you print the result of 15 * 10 ** 18:

15000000000000000000

Way bigger than the Number.MAX_SAFE_INTEGER with 20 digits.

Check the ethersjs docs here: https://docs.ethers.org/v5/api/utils/bignumber/

To solve this, you have multiple options:

1. Convert each of the numbers to the built-in Javascript BigInt type, appending an n at the end of the number:

...setUriToUpdate(15n * 10n ** 18n)...

Convert the result to a string:

contract.setUriToUpdate("15000000000000000000").

Use ethers.BigNumber.from to convert each of the factors before multiplying:

const fifteen = ethers.BigNumber.from(15);
const ten = ethers.BigNumber.from(10);
const eighteen = ethers.BigNumber.from(18);

contract.setUriToUpdate(fifteen.mul(ten).mul(eighteen)).then(response => {
    console.log("response2: ", response) 
});

And so on.

Answer 2

The error is due to the overflow and you may use BigInt data type. To use it just include

/* global BigInt */

at the top of your code file. Then use BigInt to calculate instead of the Number data type.

const bigNumber = BigInt(/*smthing*/).toString(10)

I hope it helps!