July 20, 2025 ❖ Tags: writeup, programming, webdev, javascript, artifical-intelligence
Spaced repetition is an effective habit for memorizing small fragments of information for, effectively, an indefinite amount of time. The idea is to repeatedly challenge your recall of a piece of information, typically with a sort of flashcard, doing so at a frequency determined by your previous recall performance: new information is challenged frequently until you remember it, and previously learned information is challenged less frequently. The concept is simple enough to implement with a few index cards and a shoebox. Despite the simplicity, the landscape of software implementations of spaced repetition is relatively small. The venerable Anki is the best-known spaced repetition application, and I've used org-drill and org-fc in the past, but other than those three, I'm not aware of many other programs for it. These existing systems are fine, but I have a fairly specific use-case that none are appropriate for: I might want to do my reviews on a system where I'm unable to install Anki or GNU Emacs, and I don't want to have to trust a third-party with my cards. This rules out services like Quizlet and AnkiWeb. It's a simple enough concept, so I wanted to see if I could write a flash card application contained within a single HTML file. All we really need is a spaced repetition scheduler algorithm, a way of implementing the "challenge" piece in the browser, and a way of storing cards and their scheduling parameters across reviews.