Web3.utils.fromWei silently performs unsafe conversion for big numbers because of scientific notation

[sgerodes]

Expected behavior

Web3.utils.fromWei is parsing big numbers (>=10^21) without adding an unnecessary dot

Actual behavior

Web3.utils.fromWei(19999990000000099000000, 'ether')  === "1..99999900000001e+22"
Web3.utils.fromWei(19999990000000000000000, 'ether') ===  "0.0000001.999999e+22"
Web3.utils.fromWei(19000000000000000000000, 'ether') === "0.000000000001.9e+22"

Web3.utils.fromWei insert an additional dot in the scientific notation when dealing with Big numbers
In the example below the bumber 19999999999999990000000 is parsed to ether. this correcponds to 19999.99999999999 ETH.

When parsed we can see that there is an additional dot in the output: 1.9.99999999999999e+22.
If we parse this string to a float then a 1.9 will be produced.

This behaviour silently without errors converted a number representing ca 19999 ETH to 1.9 ETH.

Steps to reproduce the behavior

import Web3 from "web3";

const wei = 19999999999999990000000; // A value bigger than 10^21
console.log(wei) // 1.999999999999999e+22
console.log(BigInt(wei)) // 19999999999999991611392n

let ethConverted = Web3.utils.fromWei(wei, 'ether');
console.log(ethConverted) // 1.9.99999999999999e+22. //  Here a string is returned with a second dot

let ethParsed = parseFloat(ethConverted);
console.log(ethParsed) // 1.9 // but should be > 19999

Logs

1.999999999999999e+22
19999999999999991611392n
1.9.99999999999999e+22
1.9

Environment

node version 20
web3.js version 4.6.0

Reason of the error

The internal logic of fromWei is behaving wrongly because the number is parsed into a scientific notation string like "1.999999999999999e+22". This inroduceses errors into the output

[SantiagoDevRel]

Thanks for posting this @sgerodes , our devs will take a look at it and reply asap!💪

[sgerodes]

The Issue comes from very large numbers (>= 10^21) are incorrectly converted into a format with an additional dot due to JavaScript's automatic scientific notation for large numbers.

Example:
String(10000000000000000000000) === '1e+22' and this messes up the fromWei function.

[sgerodes]

@SantiagoDevRel I have created a PR that fixes this Bug #6882

[SantiagoDevRel]

Amazing @sgerodes , the devs will review it tomorrow!

[jdevcs]

@sgerodes if you want to use fromWei with large number that exceeds number range use bigint as this function accepts bigint as well:

let ethConverted = Web3.utils.fromWei(BigInt(wei), 'ether');
console.log("ethConverted ",ethConverted)

> ethConverted  19999.999999999991611392

[sgerodes]

@jdevcs Thank you. That will fix my code.

But there is still a bug to be fixed. The following is clearly an errornous behaviour:

Web3.utils.fromWei(19999990000000099000000, 'ether')  === "1..99999900000001e+22"
Web3.utils.fromWei(19999990000000000000000, 'ether') ===  "0.0000001.999999e+22"
Web3.utils.fromWei(19000000000000000000000, 'ether') === "0.000000000001.9e+22"

The problem is this function accepts js non-bigint numbers greater than 10^21 and parses them incorrectly without errors or warnings.

This can create errornous behaviour. And it will occur silently.

parseFloat(Web3.utils.fromWei(19999999999999990000000, 'ether')) === 1.9 // but should equal 19999.99999999999

19999 ETH was parsed as 1.9 ETH with little code, that felt very intutive. Just using parseFloat. Which probably many of the devs use after they receive a string from "fromWei".

[sgerodes]

@jdevcs My implementation fixes all of those Issues. I have implemented a very straightforward and simple fix for that. #6882