How to format balance?

Question

I tried using @polkadot/util's formatBalance function to get the formatted balance of the account. But it doesn't make sense.

I believe unit conversion is not working properly and I wonder what I am doing wrong.

await this.api?.query.system.account('5C8Nk6HL1eYNu3NADXDGzARdNYv6uuqoQ2FCQH26odo3Tpvt', ({ nonce, data: balance }) => {
  console.log('balance:', balance.free.toHuman())
  const free = this.formatBalance(balance.free.toHuman().replace(',', '')).split(' ');
  console.log('$balanceChanges', `{"free": "${free[0]}", "freeUnit": "${free[1]}", "reserved": "${balance.reserved.toHuman()}", "nonce": "${nonce.toHuman()}"}`);
});

balance: 399,999,874,999,852 // should be 399 nanoDES
$balanceChanges {"free": "399.9986", "freeUnit": "mDES", "reserved": "0", "nonce": "4"}

balance: 1,000,399,999,874,999,852 // should be 1 DES
$balanceChanges {"free": "99.9639", "freeUnit": "kDES", "reserved": "0", "nonce": "4"}

balance: 99,399,999,499,999,407 // should be 99.39 milliDES
$balanceChanges {"free": "993.9869", "freeUnit": "DES", "reserved": "0", "nonce": "7"}

> this.api?.registry.chainDecimals
[18]

import { BN, formatBalance as mFormatBalance } from '@polkadot/util';

...

formatBalance(balance: number | string | BN | bigint): string {
    return mFormatBalance(balance, { withUnit: 'DES' }, this.api?.registry.chainDecimals[0]);
}

Answer 1

Good question. You could try something like this:

import { ApiPromise, WsProvider } from '@polkadot/api';
import { BN, formatBalance } from '@polkadot/util';

const formatAccountBalance = async () => {
    const wsProvider = new WsProvider('wss://rpc.polkadot.io');
    const api = await ApiPromise.create({ provider: wsProvider });
    const { nonce, data: balance } = await api.query.system.account('14RYaXRSqb9rPqMaAVp1UZW2czQ6dMNGMbvukwfifi6m8ZgZ');
    const chainDecimals = api.registry.chainDecimals[0];
    console.log('raw balance:', balance.free.toNumber())
    formatBalance.setDefaults({ unit: 'DOT' });
    const defaults = formatBalance.getDefaults();
    const free = formatBalance(balance.free, { withSiFull: true }, chainDecimals);
    const reserved = formatBalance(balance.reserved, { withSiFull: true }, chainDecimals);
    console.log('Formatted balance:', `{"free": "${free}", "unit": "${defaults.unit}", "reserved": "${reserved}", "nonce": "${nonce.toHuman()}"}`);
}

Should output something like this:

raw balance: 562262999731
Formatted balance: {"free": "56.2262 DOT", "unit": "DOT", "reserved": "220.2580 DOT", "nonce": "21"}

Shawn also wrote about this here:

• https://stackoverflow.com/questions/64210673/how-do-you-format-balances-with-the-polkadot-js-api

There are also nice examples here:

• https://github.com/polkadot-js/common/blob/master/packages/util/src/format/formatBalance.spec.ts