Migrating an Apache Flex app to React: Milestone 1

Last year, I mentioned that I’m migrating an Apache Flex application to JS/HTML/CSS. At the time, I was still very early in the process. I knew that I’d be using TypeScript and React by that point, but I was still evaluating various UI component libraries. In addition to learning and prototyping, I also had to port a lot of code that wasn’t part of the UI, so I haven’t had much to share about my progress until recently.

Yesterday, I deployed the first bit of code from the new version of my app Logicly to production. The original codebase included something that I call the “Logicly Viewer”, which is a limited version of the project that can be embedded in HTML to load a file in read-only mode. I created it so that I could embed a real circuit simulation into the documentation to help make various concepts more clear. Unlike the main editor, nothing in Logicly Viewer can be added, deleted, or dragged around. However, you can interact with certain components to update the simulation and watch signals propgate. I knew right away that the Logicly Viewer would make a perfect first milestone because I wouldn’t need to implement Logicly in its entirely. All of the work on this milestone will act as a foundation for future milestones, and I get to deploy something to production that real users will be able to see today while I continue to work on the rest of the project. That really helps keep me motivated!

I’ve embedded the Logicly Viewer below, with a simulation of a half adder:

(Click/tap the switches on the left side to see the simulation update)

Logicly simulates logic gates, which are low level constructs in computers and electronics that perform boolean math (operations on 1s and 0s). The simulation keeps track of the current state of a circuit, which includes the signal being output from each logic gate and where that signal gets passed next. It was relative easy to port the simulation from ActionScript to TypeScript, since the languages are so similar. However, I wanted to avoid introducing any bugs, so I ended up writing a ton of automated tests at the same time. The original implementation of the simulation in ActionScript didn’t have any tests, so writing them took a non-trivial amount of time because I had to start from scratch. It was worth it, though, because it caught a few bugs that I had accidentally introduced into the new TypeScript version.

Once the simulation was up and running, I started working on the “wires” that can be dragged between components to connect things in the simulation. You can see them in the embedded viewer above — they’re the bezier curves that are drawn between components. Implementing these as React components was an interesting challenge because it requires more access to the HTML DOM than most people using React typically need. Additionally, React’s typical data flow doesn’t play well when many components need to interact with each other from various levels of the tree. I ended up using Redux so that I could use its Provider component to connect the components with data. As for visuals, I ended up using SVG. It’s really nice to be able to use SVG right alongside HTML with JSX.

The code below basically shows how I use my wires library in React/JSX:

	<WireSurface wireFactory={this.createWireRenderer}/>

The WiresProvider is a Redux Provider component with an internal store, and it passes the data down to any components that are interested. The WireSurface is where the wires are drawn. As I mentioned, I implemented the wires as SVG bezier curves, but the WireSurface supports custom implementations that draw wires differently, if needed. The wires get the data about the connections from the WiresProvider. The components added to the <div> that appears after the WireSurface are the logic gates and other components that get displayed by the viewer/editor. These may contain child components called “terminals” where the wires start and end their connections.

The logic gates and other components are also drawn using SVG. I was able to export SVG files from my original vector art created in Adobe Animate CC. I made a few tweaks to simplify the generated SVG, but the output was actually pretty decent overall. Between JSX and CSS, modifying paths and colors in SVG at runtime turned out to be very easy. I’m excited to explore SVG further because I feel like modern web apps could really benefit, but it seems to be underutilized today.

Obviously, the Logicly Viewer needs to be able to open files created by the full version of Logicly. The underlying file format is XML, but it’s also compressed using the deflate algorithm. I ended up using the pako library to inflate the data to get the raw XML string, and I used @rgrove/parse-xml to parse the XML into JS objects. Originally, I had worried that file parsing would be a major pain. However, this ended up being one of the easiest tasks that I worked on in this project! The @rgrove/parse-xml library produced a very easy to understand object tree.

What’s next?

In the next milestone, I will start implementing the full editor with things like drag-and-drop and selection. In fact, I already have some of the drag-and-drop features implemented, since I wanted to be sure that was easy enough to implement with React before I committed. I’ll be using the excellent react-dnd library.

The next thing that I will deploy to production will be the web demo of Logicly that allows people to try the app in their browser. It currently runs on Adobe Flash Player, and #Flash2020 looms ever closer. This web demo doesn’t support saving files, printing, or opening multiple files at the same time, but everything else works the same way as the desktop app. It’ll be more work than the Logicly Viewer, I think, but it’s also another subset that allows me to deploy more to production before the whole project is completed. After that, I’ll start digging into Electron to build desktop apps for Windows, macOS, and Linux. Then, Logicly will be ready for the future, and I can explore new possibilities, like mobile apps, Chromebooks, and more!

About Josh Tynjala

Josh Tynjala is a frontend software developer, open source contributor, karaoke enthusiast, and he likes bowler hats. Josh develops Feathers UI, a user interface component library for creative apps, and he is a member of the OpenFL leadership team. One of his side projects is Logic.ly, a digital logic circuit simulator for education. You should follow Josh on Mastodon.


  1. Atanas

    Hi Josh,

    Thank you very much for sharing (as you always do)!

    I was wondering … what is the future of the brilliant FeathersUI in the context of the last sentence of the last paragraph above?



    1. Josh Tynjala

      The last sentence of the last paragraph applies specifically to Logicly. I have been working on Logicly for around ten years now, and it is a completely independent project that is separate from Feathers.

      Adobe has continued funding Feathers in 2018, but with a reduced budget. Even with less funding, I have two new versions with added features (3.5 and 3.6) planned for this year.

    1. Josh Tynjala

      It’s probably a little late to be trying to embed a .swf file on the web, considering that Adobe is discontinuing Flash Player by the end of 2020.

      However, if I had to guess, you probably need to give the <object> or <embed> HTML tag a key in your JSX. I know that I needed to do that for a <canvas> tag in one of my projects. If I didn’t, React would recreate the canvas over and over as my component re-rendered, effectively erasing what I had drawn. Once I gave it a key, my drawings persisted. I would guess that a similar solution is necessary when embedding .swf content.

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