Ethers.js BigNumber Overflow – How to Use a Contract with Wei

ethers.jsjavascriptmetamask

I made a page where you can enter an amount of token and it gets swapped to another token.
It works until I use a number above 999. My smartcontract gets wei, so I have to transform the normal number to wei with the function below.

const toWei = amount => {
    return amount * Math.pow(10, 18)
}

I get huge numbers out and I get this error

Error: invalid BigNumber string (argument="value", value="2e+21", code=INVALID_ARGUMENT, version=bignumber/5.6.0)

What can I do that this does not appear and is best practice?

Best Answer

The string "2e+21" is not valid for the BigNumber class.

JavaScript uses IEEE 754 numbers, which means any value above around 0.009 would suffer precision loss, and Ethereum is quite picky about numbers not being approximate.

You should use strings for large values, or use the convenience functions provided for converting units, such as ethers.utils.parseEther("1.0") which handles string values.

Here is more info on why you need Big Number: https://docs.ethers.io/v5/api/utils/bignumber/#BigNumber--notes-safenumbers

Related Solutions

[Ethereum] Using ether.js with metamask

Actually the answer can be found in the ethers.js doc.

Ethers.js supports web3 providers, so to get it to work metamask on browser is quite simple.

if (typeof web3 !== 'undefined') {
  var web3Provider = new ethers.providers.Web3Provider(web3.currentProvider, ethers.providers.networks.ropsten);
  web3Provider.getBalance("..some address.."). then(function(balance) {
    var etherString = ethers.utils.formatEther(balance);
    console.log("Balance: " + etherString);
  });
}

[Ethereum] use ether.js with truffle

Truffle use Web3 by default and its injected inside as global dependency. You can't get rid of it, but you can install ether.js as dependency on your project.

truffle init

then you install your module

npm install --save ethers

and eventually you use it in your truffle tests

var ethers = require('ethers');

you can use the ethers library into your tests and then execute with truffle test command.

Consider that you wouldn't have the library if you use truffle develop, since only web3 would be injected.

Best Answer

Related Solutions

[Ethereum] Using ether.js with metamask

[Ethereum] use ether.js with truffle

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