How do you format balances with the Polkadot JS API?

I would like to get the balance of a user formatted using the base unit of the Substrate chain.

When I use toHuman(), I get an opinionated formatting which includes a prefix like so:

let account = await api.query.system.account("EGVQCe73TpFyAZx5uKfE1222XfkT3BSKozjgcqzLBnc5eYo");
account.data.free.toHuman()

2.8320 kKSM

While toNumber() returns the value without any units at all:

account.data.free.toNumber()

2832057009447293

How do I get this value with just the base units using the Polkadot JS API?

You will need to query the chain for the chainDecimals, which will tell you how many places into the raw value you should place the decimal:

api.registry.chainDecimals

12

You can either directly parse the number by dividing by 10^{chainDecimals}, or you can use the Polkadot JS utility function formatBalance to help you format this a bit more easily:

formatBalance(
    accountData.data.free,
    { withSi: false, forceUnit: '-' },
    chainDecimals
);

2,832.057

I ended up making a utility function like this:

function toUnit(balance, decimals) {
    base = new BN(10).pow(new BN(decimals));
    dm = new BN(balance).divmod(base);
    return parseFloat(dm.div.toString() + "." + dm.mod.toString())
}