@ssense/number-utils

Usage

Decimal

The type allows to explicitely define precision in contracts/interfaces.

import { Decimal } from '@ssense/number-utils';

export interface OrderTaxes {
    code: string;
    rate: Decimal<6>;
    totalAmount: Decimal<2>;
    details: {
        rate: Decimal<6>;
        name: string;
        amount: Decimal<2>;
    }[];
}

ToDecimal

Why use this function: Naive implementations like parseFloat(num.toFixed(2)) will lead to rounding inconsistencies. eg. parseFloat(436.905.toFixed(2)) = 436.90 instead of 436.91

ToDecimal rounds precisely by acounting for floating point arithmetic inconsistencies. It returns Decimal.

import { NumberUtils } from '@ssense/number-utils';

const subtotal = 75;
const taxRate = 0.14975;
const total = subtotal * (1 + taxRate); // 89.8125

// We cant charge less than 1 cent, hence, the total has to be rounded
const displayedTotal = NumberUtils.toDecimal<2>(total, 2); // 89.81

If interested in learning more on how this works:

• This guide covers Floating-Point Arithmetic
• This stackoverflow answer shows concrete examples