[Ethereum] How to safely manage WEI units

web3js

I'm confused about how to manage/calculate with WEI in a web3 application.

So far I found:

BigInt: This is JS native and it works with large quantities (e.g. 10000000000000000000000). But it doesn't have out of the box utilities like e.g. converting to hex.
BigNumber: This is provided by ethers:

Many operations in Ethereum operation on numbers which are outside the range of safe values to use in JavaScript.
A BigNumber is an object which safely allows mathematic operations on numbers of any magnitude.

Given this description, and that it's dedicated to Ethereum, I thought this must be it, but it actually doesn't work with large numbers:

// Numbers outside the safe range fail:
BigNumber.from(Number.MAX_SAFE_INTEGER);
// Error: overflow (fault="overflow", operation="BigNumber.from", value=9007199254740991, code=NUMERIC_FAULT, version=bignumber/5.0.8)

Aside of that, for WEI I probably need integers, not floating point.

So what's the recommended way to deal with WEI?

In the ideal case I'd like something that not only represent big numbers but actual WEIs and has built in functionality to convert safely to and calculate with GWEI or ETH out of the box, but this is not a must.

Using Typescript, but it probably isn't relevant.

Edit: I found another library: BigNumber.js. This seems to do what I expect. It can be converted to string to interact with web3.js.

Best Answer

BigNumber is the recommended way to go. Probably it has much better support than various BigInt libraries.

There are lots of BigNumber libraries out there and I guess most of them provide very similar functionality. So probably almost any of them will work just fine for you.

At least ethers.js has a built-in BigNumber support so no need to look any further if you happen to use that library.

When you have your BigNumber library you can get regular token amounts with something like this (taken from one of my ERC20 token deployment scripts):

var exp = ethers.BigNumber.from("10").pow(18);
const supply = ethers.BigNumber.from("50").mul(exp);

Related Solutions

[Ethereum] Web3 – how to add WEI and ETH values correctly

You are concatenating strings in JavaScript.

Here is what happens:

var test = "he";
var test2 = "llo";
console.log(test+test2);

OUTPUTS: hello. You are using integers as strings.

Therefore you need to convert your variables to int before adding them.

Here is an example:

highestBidAmount = parseInt(highestBidAmount, 10);

Sidenote: Don't change the 10 it has nothing to do with decimal places. It's the radix used.

Do that with both variables:

minBidIncrement = parseInt(minBidIncrement, 10);

Now add them:

let minNextBid = highestBidAmount + minBidIncrement;

Now you are adding integers so it results in: 200000000000000000

Convert wei value of USDC balance to proper number

The fromWei function converts from wei to ether, meaning it divides the number by 1e18.

ERC20 tokens allows a custom decimal point precision, USDC specifically uses 6 decimal precision. So you just need to divide your result by 1e6 -

const balance = parseInt(result) / 10**6;

But ideally, to support any ERC20 token, read the number of decimals from the contract and use that; also better use a library that knows how to work with big numbers, because JS has issues when it comes to big/real numbers.

async function getBalance() {
   const result = await contract.methods.balanceOf(walletAddress).call();
   const decimals = await contract.methods.decimals().call();
   const balance = new BigNumber(result).div(10 ** decimals);
   return balance;
}

Best Answer

Related Solutions

[Ethereum] Web3 – how to add WEI and ETH values correctly

Convert wei value of USDC balance to proper number

Related Topic