Femto-FSRS

A zero dependency implementation of the FSRS 4.5 spaced repetition algorithm.

I am building this library as a replacement to SM-2 in KoalaSRS.

Demo

I made an HTML pen-and-paper demo here. You can store facts on paper and use Femto-FSRS for scheduling, just like Piotr Wozniak did in the 80s.

Features

• Zero dependencies
• Well annotated source code that (mostly) follows the paper.
• Sensible defaults.

Usage

import { Grade, createDeck } from "femto-fsrs";

// === Create a new deck
const { newCard, gradeCard } = createDeck();

// === Initiate a new card with an initial grade of "GOOD":
const initialGrade = Grade.GOOD;
const myCard = newCard(initialGrade);

// === Grade the card as "easy" two days later.
//     Returns a new card that replaces the old one.
const daysSinceReview = 2;
const nextCard = gradeCard(myCard, daysSinceReview, Grade.EASY);
// The "I" attribute represents "I" like in the FSRS paper.
// It is the next review date at which the probability
// of success is 90% (assuming you used default parameters).
const nextReview = nextCard.I.toFixed(2);
// Print results:
console.log(`Card will be due for review in ${nextReview} day(s)`);

Result:

Card will be due for review in 16.63 day(s)

Installation

npm install femto-fsrs

Not Included

This is supposed to be a minimalistic library that can be used as a starting point for FSRS-enhanced apps. If you need a more full-featured offering with features like logs (so you can optimize your w param) or revert, etc.., check out ts-fsrs.

Tests

npm run test