This is a basic streak counter - inspired by Duolingo - written in TypeScript and meant for the browser (uses localStorage).
yarn add @orlenka/streak-counter
import {streakCounter} from '@orlenka/streak-counter'
const today = new Date();
const streak = streakCounter(localStorage, today);
// streak returns an object:
// {
// currentCount: 1,
// lastLoginDate: "11/11/2021",
// startDate: "11/11/2021"
// }