How to convert BigNumber to Number in Truffle framework?

Question

I have written an ERC20 token contract and deployed it in test network using truffle framework. When I check the token balance for an account using web3 it was giving the result in BigNumber when I try to convert it to a number using toNumber() getting an unexpected result.

Solidity code:

  function balanceOf(address _from) constant public returns (uint256 balance) {
    return balances[_from];
}

Javascript code:

instantiateBalance() {
const contract = require('truffle-contract')
const token = contract(Token)
token.setProvider(this.state.web3.currentProvider)
var tokenInstance;
token.deployed().then(function(instance) {
tokenInstance = instance;
return tokenInstance.balanceOf.call("0xb1Cf866ced575FD1A1997Daa5d6F099efb282E41", {from: "0xb1Cf866ced575FD1A1997Daa5d6F099efb282E41"});
}).then(function(balance) {
console.log(balance.toNumber());
})

Expected Result

Decimals = 18

Actual Token Balance = 100000000.000000000000000000

Actual Result

Token Balance = 1000000000000

did you try balance.div(1e18) or balance.toNumber().div(1e18) ? — Rajesh, Oct 31 '17 at 05:16
balance.div(1e18) will give me the digits before the decimal point. I need digits after decimal point also to display exact balance. — Karthikeyan Thangavel, Oct 31 '17 at 06:37

score 27 · Accepted Answer · edited Nov 10 '18 at 23:09

27

If your token have 18 decimals

like an ether you can use

then(function(balance) {
    console.log(web3.fromWei(balance.toNumber(), "ether" ) );
})

Use fromWei to convert your bigNumber to ether and then convert it to Number. Be aware that unnecessary 0 after the floating point will not be displayed.

In web3 ^1.0 it may change to web3.utils.fromWei instead of web3.fromWei doc. Note that truffle ^5.0 uses web3 ^1.0.

If you have a different token decimal

Let's say 6. You'll have to do the conversion manually with something like:

var tokenBalance = balance.ToNumber() / Math.pow(10, tokenDecimals)

edited Nov 10 '18 at 23:09

Paul Razvan Berg

17,902
6
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143

answered Oct 31 '17 at 09:05

0xCrema.eth

1,182
1
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21

1

I experienced a problem with this example, if the balance had 18 decimals it would strip it back to 16. To fix this I used web3.fromWei(balance.toString(), "ether"), notice .toString(). I'm unsure if this is best practice. – Sean Bannister Feb 21 '18 at 14:53
yes using toString() worked for me as well, when I used toNumber(), it gave me an error because we can not store that big number in that data type I think. – Zeeshan Ahmad Khalil Dec 24 '19 at 18:25
ToNumber not a function in truffle – Philip Rego Sep 07 '20 at 17:40
@PhilipRego this was answered 3 years ago. It's obvious it changed now. – 0xCrema.eth Sep 09 '20 at 15:19
From Etherjs BigNumber.from(bn).div(BigNumber.from(10).pow(decimal)).toNumber() – Sedhu Dec 16 '21 at 05:15

Nikita · Answer 2 · 2018-10-01T11:55:44.987

7

You can use exponential number syntax in javascript to shorten you code.

Example (18 decimals):

const balance = getBalance().toNumber() / 1E18

PS. Sorry, i can not make comment due to low reputation.

edited Oct 01 '18 at 11:55

answered Sep 30 '18 at 18:40

Nikita

189
1
3

score 3 · Answer 3 · answered Sep 18 '19 at 11:44

Personally, I like to work with big numbers and not parse them into "normal" numbers. I guess I'm afraid some overflow may happen if I don't.

Therefore, if a contract returns a uint, then I parse the return value to a BigNumber (from bignumber.js), like so:

const balanceBefore = new BigNumber(await contract.getBalance(...));

and I like to use the BigNumber API for my assertions, like so:

assert(balanceBefore.minus(amountSent).minus(gasCost).isEqualTo(balanceAfter));

If you -1 please also add a comment with the reason why ... thank you. — Ytsen de Boer, Sep 08 '20 at 10:06

score 0 · Answer 4 · answered Dec 24 '21 at 12:19

0

I believe you just want log the balance, you should use

    console.log(balance.toString());

instead.

It's throws genuine error that it can't fit the number in js number type.

answered Dec 24 '21 at 12:19

Abhishek Kumar

101
1

score 0 · Answer 5 · answered Sep 11 '20 at 20:00

A fast way could be

import web3 from 'web3';
const ethProvider = new web3(web3.givenProvider).eth;
const accounts = await ethProvider.requestAccounts();
const ethBalance = web3.utils.fromWei(await ethProvider.getBalance(accounts[0]), 'ether');
console.log(ethBalance);

How to convert BigNumber to Number in Truffle framework?

5 Answers5

If your token have 18 decimals

If you have a different token decimal

Example (18 decimals):

Linked