Offline APL - Making ngn/apl a Mobile PWA
Hey everyone! Recently, my pull request (PR) to add offline Progressive Web App (PWA) capability to ngn/apl was accepted. I wanted to share how I went about making this open source contribution. But before we go further, feel free to check out the ngn/apl website - you can install it as an offline PWA app like this.
For those unfamiliar, 
APL is a niche programming language I’ve recently been exploring. It’s a quirky, concise language that grows on you after a while. It’s even more concise than Python, which says a lot! You can check out my notes and APL resources, which I compiled while learning APL.
Fun Fact⚡: both NumPy and Pandas were partially inspired by APL, as it was the first array-oriented language. To get an idea of how concise APL can be, check out Conway’s Game of Life in APL, in which one line of APL is doing work that would take a page of Python code!
So, why did I decide to add offline PWA support to ngn/apl? I often find myself with some free time while traveling, and I love to tinker with APL. However, internet connectivity is often unreliable on the go. That’s why I wanted ngn/apl to be installable as a PWA that works offline. To get started, I read up on Progressive Web Apps and how to implement them. This mainly involved creating a manifest.json file and figuring out how to cache assets for offline use using serviceWorker.js - check out its code. Luckily, this was possible with ngn/apl because the server’s role is minimal; it only serves the initial HTML/CSS/JS. The APL interpreter runs entirely in the frontend JavaScript, so no backend APIs are needed. This isn’t the case with other APL interpreters like TryAPL, which rely on backend APIs for interpretation.
When I decided to implement this feature, I forked the ngn/apl repo and started working on it. Initially, I faced some challenges, particularly with caching not working as expected. This pushed me to dive deeper into service worker JavaScript to ensure everything worked smoothly offline. A few days ago, I shared my fork in the APL Farm (Discord) community, and the maintainer asked why I hadn’t opened a PR for it. I explained that I thought the original repo was abandoned. He encouraged me to submit a PR, and after making some formatting adjustments to match the original code style, my PR was accepted!
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