modulo

modulo defines the mathematical modulo operation in TypeScript for Deno.
— eibens/modulo on GitHub

Motivation

JavaScript has no native support for true modulo. The % operator works as modulo for positive numbers, but not negative ones. For example, -1 % 3 = -1 compared to -1 mod 3 = 2. If you need the latter, you can either use this module, or memorize this modulo formula for JavaScript:

n mod m = ((n % m) + m) % m

mod.ts

The modulo function calculates p = n mod m:

import { modulo } from "./mod.ts";

const n = -1;
const m = 3;
const p = modulo(n, m);

const test = p === 2;
if (!test) throw new Error();

The quotient function calculates q = floor(q / m).

import { modulo, quotient } from "./mod.ts";

const n = -1;
const m = 3;
const q = quotient(n, m);

const test = q === -1;
if (!test) throw new Error();

The decompose function calculates (q, p). q, m, and p together define the original value n = q * m + p:

import { decompose } from "./mod.ts";

const n = -1;
const m = 3;
const [q, p] = decompose(n, m);

const test = n == q * m + p;
if (!test) throw new Error();