从 JavaScript 中的数字中减去增值税

Question

I am beginner in JS and this code

$('.brutto_amount').each(function (index, value) {
    let amount = $(this).text().replace(' brutto / rok', '').replace('(', ''); console.log(amount);
    if (discountType == 0) {
        let newAmount = (amount - discountValue).toFixed(2);
        if(newAmount < 0) newAmount = 1;
        $(this).html(`${newAmount} brutto / rok `);
    } else if (discountType == 1) {
        let newAmount = (amount - ((parseInt(amount) * parseInt(discountValue)) / 100)).toFixed(2);
        if(newAmount < 0) newAmount = 1;
        $(this).html(`${newAmount} brutto / rok `);
    }
});

works fine so far.

How can I subtract 23% VAT from the variable newAmount and round it to 2 decimal places?

Answer 1

I solved the problem similar to what Lapskaus mentions in the comments :

The first is a simple math problem, if your newAmount value is a brutto value, calculating the netto, with a vat of 23%, is as simple as newAmount / 123 * 100 . Use calculatedNetto.toFixed(2) to round that to 2 numbers. Be aware though, that calculations in JS will have rounding errors due to floating point precision. For further information about the issue and how to circumvent that, read this . newAmount will be a brutto value which will be 123% from which you want to calculate the 100% value. You substract 23% off of 123 which is too much