Dinero expects amounts as number by default. In most cases, this is more than enough, but there are times when you might hit the limitations of the biggest and smallest numbers you can safely represent.
A typical use case is when you need to represent colossal amounts of money. Take the world debt, which reached $258 trillion in 2020. In JavaScript, the biggest number you can accurately represent is 9007199254740991 (9 quadrillions and some spare change). Still, since Dinero requires you to pass amounts in minor currency units, you actually "lose" two orders of magnitude, and can only represent around $90 trillion.
import { dinero } from 'dinero.js';
import { USD } from '@dinero.js/currencies';
// Don't do this!
// 25800000000000000 is too big for accurate representation
// in IEEE 754 numbers.
const price = dinero({ amount: 25800000000000000, currency: USD });
Another example is when you need to represent cryptocurrencies, which typically have high exponents. In 2021, the Ether can be subdivided down to 18 fraction digits, meaning you can't even represent 1 ETH with the number type.
import { dinero } from 'dinero.js';
const ETH = {
code: 'ETH',
base: 10,
exponent: 18,
};
// Don't do this!
// 1000000000000000000 is too big for accurate representation
// in IEEE 754 numbers.
const price = dinero({ amount: 1000000000000000000, currency: ETH });
In such cases, you need to rely on safer alternatives, such as the bigint primitive or third-parties like big.js.
Copy linkUsing Dinero with bigint
Dinero provides a bigint calculator for you to use out of the box. You can create your own dinero function by passing the calculator to the createDinero factory.
import { calculator } from '@dinero.js/calculator-bigint';
import { createDinero } from 'dinero.js';
const dineroBigint = createDinero({ calculator });
You can then use this function to create Dinero objects and manipulate them with any Dinero function. Keep in mind that once you're in bigint land, every numeric value you pass needs to be a bigint as well.
import { add } from 'dinero.js';
const USD = {
code: 'USD',
base: 10n,
exponent: 2n,
};
const d1 = dineroBigint({ amount: 500n, currency: USD });
const d2 = dineroBigint({ amount: 100n, currency: USD });
add(d1, d2); // a Dinero object with amount `600n`
Copy linkUsing Dinero with a custom amount type
Dinero.js delegates all calculations to a type-specific calculator object. The calculator fully determines what amount type you can pass to Dinero objects. Therefore, by changing the calculator with one of a different type, you can create Dinero objects of this type.
You can implement your own if you want to use a third-party library.
Copy linkImplementing a custom calculator
Dinero.js delegates all calculations to a type-specific calculator object. You can implement a custom calculator for a given type and pass it to Dinero to use the library with amounts of this type.
A calculator implements the Calculator interface. For example, here's what it can look like with big.js.
import Big from 'big.js';
import { Calculator, ComparisonOperator } from 'dinero.js';
const calculator: Calculator<Big> = {
add: (a, b) => a.plus(b),
compare: (a, b) => a.cmp(b) as unknown as ComparisonOperator,
decrement: (v) => v.minus(new Big(1)),
increment: (v) => v.plus(new Big(1)),
integerDivide: (a, b) => a.div(b).round(0, Big.roundDown),
modulo: (a, b) => a.mod(b),
multiply: (a, b) => a.times(b),
power: (a, b) => a.pow(Number(b)),
subtract: (a, b) => a.minus(b),
zero: () => new Big(0),
};
Once you have your calculator, you can build a custom dinero function.
import { createDinero } from 'dinero.js';
// ...
const bigDinero = createDinero({ calculator });
You might notice that you're passing the full calculator, meaning you're shipping calculator methods you might not use. This is unlikely to represent a bottleneck, especially if you're using Dinero with a third-party library like big.js because you're only referencing methods that already exist on every Big object you create.
Copy linkPicking the right amount type
Depending on what you use Dinero.js for, you might want to choose a different amount type better suited to your needs. Knowing what to pick depends on your constraints, use case, and what compromises you can to make.
With amount types, the main trade-off is between precision and performance. Safe arbitrary precision comes at the cost of speed, so you need to properly assess your needs before deciding.
Copy linkWhen to use number
By default, Dinero.js uses the number type. It's ideal when you need to express monetary values that will never exceed what the type can safely represent.
The number primitive type lets you create double-precision floats (or "doubles") using the IEEE 754 standard. It works well for many use cases and provides excellent performance. However, doubles can only represent a limited range of numbers (from -(2^53 - 1) to 2^53 - 1). Anything below or above gets truncated when converted to binary and stored in memory, resulting in imprecisions.
Using Dinero.js with numbers works well when you know and control the numbers to represent. It works for many use cases including dynamic pricing pages, ecommerce sites, or money management applications, as long as you're confident you'll never exceed the type limitations.
Copy linkBenefits
- Great performance, implemented in hardware
- Full browser and Node.js compatibility (requires some polyfills for some static and
Mathfunctions)
Copy linkDrawbacks
- Limited range of numbers that can be accurately represented
Copy linkWhen to use bigint
Dinero.js provides a bigint calculator, allowing you to use the library with native bigints. It's ideal when you need to represent monetary values with large amounts, beyond what the number type safely supports.
The bigint primitive type lets you create arbitrarily large integers and ensures arithmetic precision. However, bigints are much slower than numbers, and not available in all environments. They're also impossible to polyfill and hard to transpile without incurring significant performance costs.
Using Dinero.js with the bigint type is recommended when you need to use numbers that exceed the number limitations. It can also act as a safeguard when you don't control the monetary amounts in your app, and you have reasons to believe you might exceed the limits. This applies to use cases such as cryptocurrency or stock trading applications.
Copy linkBenefits
- Arbitrary-precision integer support
- Faster than any userland arbitrary-precision library (see Chrome benchmark)
Copy linkDrawbacks
- Significantly slower than
numbers, implemented in software - Impossible to polyfill directly or to efficiently transpile down to ES5
- No native
JSON.stringifyandJSON.parsesupport, requires a custom replacer and reviver
Copy linkWhen to use libraries
If you need to support arbitrarily large integers in browsers that don't support bigints, you can write a custom calculator to use Dinero.js with libraries like big.js or JSBI.
Contrary to the bigint type which relies on operators, libraries expose APIs to safely manipulate arbitrarily large integers. Such solutions usually rely on strings or arrays of numbers, making them more widely supported across browsers. However, this has a significant impact on performance because of the extra runtime logic, algorithmic complexity, and increase in bundle size.
Using Dinero.js with arbitrary precision arithmetic libraries makes sense when you wish you could use bigints but cannot because you need to support environments that don't implement them.
Copy linkBenefits
- Better browser and Node.js support than
bigints, transpilable and polyfillable
Copy linkDrawbacks
- Significantly slower than
numbers andbigints - Increase in bundle size, impacting download and parse time
Dinero.js doesn't endorse any specific arbitrary precision library, or guarantees they work correctly. If you need to use a library, make sure to verify it works as expected.