modulo

modulo implements the mathematical modulo operation in TypeScript for Deno.

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:

x mod n = ((x % n) + n) % n

mod.ts

The modulo function calculates m = x mod n:

import { modulo } from "https://deno.land/x/modulo/mod.ts";

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

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

The quotient function calculates q = floor(x / n).

import { modulo, quotient } from "https://deno.land/x/modulo/mod.ts";

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

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

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

import { decompose } from "https://deno.land/x/modulo/mod.ts";

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

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