Note that all the applications share the same library, which, for historical reasons, is in `ReactNativeClient/lib`. This library is copied to the relevant directories when building each app.
First you need to setup React Native to build projects with native code. For this, follow the instructions on the [Get Started](https://facebook.github.io/react-native/docs/getting-started.html) tutorial, in the "React Native CLI Quickstart" tab.
To test the extension please refer to the relevant pages for each browser: [Firefox](https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension#Trying_it_out) / [Chrome](https://developer.chrome.com/extensions/faq#faq-dev-01). Please note that the extension in dev mode will only connect to a dev instance of the desktop app (and vice-versa).
To make changes to the application, you'll need to rebuild any TypeScript file you've changed, and rebuild the lib. The simplest way to do all this is to watch for changes from the root of the project. Simply run this command, and it should take care of the rest:
You can specify additional parameters when running the desktop or CLI application. To do so, add `--` to the `npm start` command, followed by your flags. For example:
Most of the application is written in JavaScript, however new classes and files should generally be written in [TypeScript](https://www.typescriptlang.org/). All TypeScript files are generated next to the .ts or .tsx file. So for example, if there's a file "lib/MyClass.ts", there will be a generated "lib/MyClass.js" next to it. It is implemented that way as it requires minimal changes to integrate TypeScript in the existing JavaScript code base.
If you'd like to auto-reload the desktop app on changes rather than having to quit and restart it manually each time, you can use [watchman-make](https://facebook.github.io/watchman/docs/watchman-make.html):
It still requires you to quit the application each time you want it to rebuild, but at least you don't have to re-run `"npm start"` each time. Here's what the workflow loop looks like in practice:
Please read for the [Build Troubleshooting Document](https://github.com/laurent22/joplin/blob/master/readme/build_troubleshooting.md) for various tips on how to get the build working.