SuperMemo

A JavaScript/TypeScript implementation of the SuperMemo 2 (SM2) algorithm for spaced based repetition flashcards.

Explanation

type SuperMemoItem = {
  interval: number;
  repetition: number;
  efactor: number;
};

type SuperMemoGrade = 0 | 1 | 2 | 3 | 4 | 5;

supermemo(item: SuperMemoItem, grade: SuperMemoGrade): SuperMemoItem

• item
  • repetition: the number of continous correct responses. The initial repetition value should be 0.
  • interval: inter-repetition interval after the repetitions (in days). The initial interval value should be 0.
  • efactor: easiness factor reflecting the easiness of memorizing and retaining a given item in memory. The initial efactor value should be 2.5.
• grade:
  • 5: perfect response.
  • 4: correct response after a hesitation.
  • 3: correct response recalled with serious difficulty.
  • 2: incorrect response; where the correct one seemed easy to recall.
  • 1: incorrect response; the correct one remembered.
  • 0: complete blackout.

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Installation

For Browser

import { supermemo } from 'https://esm.sh/supermemo@2';

For Node

npm install --save supermemo

CommonJS

const { supermemo } = require('supermemo');

ES Modules

import { supermemo, SuperMemoItem, SuperMemoGrade } from 'supermemo';

For Deno

deno add jsr:@vien/supermemo

import { supermemo, SuperMemoItem, SuperMemoGrade } from '@vien/supermemo';

OR

import { supermemo, SuperMemoItem, SuperMemoGrade } from 'jsr:@vien/supermemo';

Usage

let item: SuperMemoItem = {
  interval: 0,
  repetition: 0,
  efactor: 2.5,
};

console.log(item);

item = supermemo(item, 5);
console.log(item);

item = supermemo(item, 4);
console.log(item);

How to implement SuperMemo with DayJS?

import dayjs from 'dayjs';
import { supermemo, SuperMemoItem, SuperMemoGrade } from 'supermemo';

interface Flashcard extends SuperMemoItem {
  front: string;
  back: string;
  dueDate: string;
}

function practice(flashcard: Flashcard, grade: SuperMemoGrade): Flashcard {
  const { interval, repetition, efactor } = supermemo(flashcard, grade);

  const dueDate = dayjs(Date.now()).add(interval, 'day').toISOString();

  return { ...flashcard, interval, repetition, efactor, dueDate };
}

let flashcard: Flashcard = {
  front: 'programer',
  back: 'an organism that turns caffeine in software',
  interval: 0,
  repetition: 0,
  efactor: 2.5,
  dueDate: dayjs(Date.now()).toISOString(),
};

console.log(flashcard);

flashcard = practice(flashcard, 5);
console.log(flashcard);

flashcard = practice(flashcard, 3);
console.log(flashcard);

Experience

I work remotely, so improving my English is a constant challenge. I needed a way to expand my vocabulary and actually remember it.

That’s when I found the SuperMemo algorithm. It made sense. Spaced repetition helps lock words into long-term memory. So, I built this JavaScript/TypeScript library from the original Delphi code.

Then, I took it further—created a side project using React.js, Next.js and Hasura GraphQL. I used it to practice common words. Over time, I memorized more than 10,000 words. It worked.

After seeing the results, I turned it into a product to help others do the same. But it failed. Maybe I wasn’t good at marketing. Maybe most learners don’t have the patience I did.

Still, I learned something: a good method isn’t enough. People need the right mindset, too. Would I do it again? Probably. Because every failure teaches something new.

References

• The explanation of SuperMemo 2 Algorithm
• The Delphi implementation of SuperMemo 2 Algorithm