Expensify.cash

Table of contents

• Local Development
• Running The Tests
• Debugging
• Structure of the app
• Philosophy
• Deploying

Additional Reading

• Contributing to Expensify.cash
• Expensify Code of Conduct
• Contributor License Agreement

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Local development

These instructions should get you set up ready to work on Expensify.cash 🙌

Getting Started

1. Install node & npm: brew install node
2. Install watchman: brew install watchman
3. Install dependencies: npm install

You can use any IDE or code editing tool for developing on any platform. Use your favorite!

Running the web app 🕸

• To run the development web app: npm run web
• Changes applied to Javascript will be applied automatically via WebPack as configured in webpack.dev.js

Running the iOS app 📱

• To install the iOS dependencies, run: npm install && cd ios/ && pod install && cd ..
• To run a on a Development Simulator: npm run ios
• Changes applied to Javascript will be applied automatically, any changes to native code will require a recompile

Running the Android app 🤖

• To install the Android dependencies, run: npm install, then gradle will install all linked dependencies
• To run a on a Development Emulator: npm run android
• Changes applied to Javascript will be applied automatically, any changes to native code will require a recompile

Running the MacOS desktop app 🖥

• To run the Development app, run: npm run desktop, this will start a new Electron process running on your MacOS desktop in the dist/Mac folder.

Troubleshooting

1. If you are having issues with Getting Started, please reference React Native's Documentation
2. If you are running into issues communicating with the API please verify your .env file is set up correctly for the platform you are trying to run.

Note: Expensify engineers that will be testing with the API in your local dev environment please refer to these additional instructions.

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Running the tests

Unit tests

Unit tests are valuable when you want to test one component. They should be short, fast, and ideally only test one thing. Often times in order to write a unit test, you may need to mock data, a component, or library. We use the library Jest to help run our Unit tests.

• To run the Jest unit tests: npm run test

End to end tests

End to end tests are valuable when we do not want to mock data and run against the actual compiled app on iOS or Android. In order to run the end to end tests, we have to compile the iOS or Android app, then launch a simulator, then run tests. We use Detox a "Gray box end-to-end testing and automation library" to help with our end to end testing.

You are first required to build the tests, then you can run them:

1. To build the Detox end to end tests: npm run detox-build
2. To run the Detox end to end tests: npm run detox-test

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Debugging

iOS

1. If running on the iOS simulator pressing ⌘D will open the debugging menu.
2. This will allow you to attach a debugger in your IDE, React Developer Tools, or your browser.
3. For more information on how to attach a debugger, see React Native Debugging Documentation

Android

Our React Native Android app now uses the Hermes JS engine which requires your browser for remote debugging. These instructions are specific to Chrome since that's what the Hermes documentation provided.

1. Navigate to chrome://inspect
2. Use the Configure... button to add the Metro server address (typically localhost:8081, check your Metro output)
3. You should now see a "Hermes React Native" target with an "inspect" link which can be used to bring up a debugger. If you don't see the "inspect" link, make sure the Metro server is running.
4. You can now use the Chrome debug tools. See React Native Debugging Hermes

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Structure of the app

These are the main pieces of the application.

Onyx

This is a persistent storage solution wrapped in a Pub/Sub library. In general that means:

• Onyx stores and retrieves data from persistent storage
• Data is stored as key/value pairs, where the value can be anything from a single piece of data to a complex object
• Collections of data are usually not stored as a single key (eg. an array with multiple objects), but as individual keys+ID (eg. report_1234, report_4567, etc.). Store collections as individual keys when a component will bind directly to one of those keys. For example: reports are stored as individual keys because OptionRow.js binds to the individual report keys for each link. However, report actions are stored as an array of objects because nothing binds directly to a single report action.
• Onyx allows other code to subscribe to changes in data, and then publishes change events whenever data is changed
• Anything needing to read Onyx data needs to:
  1. Know what key the data is stored in (for web, you can find this by looking in the JS console > Application > local storage)
  2. Subscribe to changes of the data for a particular key or set of keys. React components use withOnyx() and non-React libs use Onyx.connect().
  3. Get initialized with the current value of that key from persistent storage (Onyx does this by calling setState() or triggering the callback with the values currently on disk as part of the connection process)
• Subscribing to Onyx keys is done using a constant defined in ONYXKEYS. Each Onyx key represents either a collection of items or a specific entry in storage. For example, since all reports are stored as individual keys like report_1234, if code needs to know about all the reports (eg. display a list of them in the nav menu), then it would subscribe to the key ONYXKEYS.COLLECTION.REPORT.

Actions

Actions are responsible for managing what is on disk. This is usually:

• Subscribing to Pusher events to receive data from the server that will get put immediately into Onyx
• Making XHRs to request necessary data from the server and then immediately putting that data into Onyx
• Handling any business logic with input coming from the UI layer

The UI layer

This layer is solely responsible for:

• Reflecting exactly the data that is in persistent storage by using withOnyx() to bind to Onyx data.
• Taking user input and passing it to an action

Directory structure

Almost all the code is located in the src folder, inside it there's some organization, we chose to name directories that are created to house a collection of items in plural form and using camelCase (eg: pages, libs, etc), the main ones we have for now are:

• components: React native components that are re-used in several places.
• libs: Library classes/functions, these are not React native components (ie: they are not UI)
• pages: These are components that define pages in the app. The component that defines the page itself should be named <pageName>Page if there are components used only inside one page, they should live in its own directory named after the <pageName>.
• styles: These files define styles used among components/pages

File naming/structure

Files should be named after the component/function/constants they export, respecting the casing used for it. ie:

• If you export a constant named CONST it's file/directory should be named the CONST.
• If you export a component named Text the file/directory should be named Text
• If you export a function named guid the file/directory should be named guid.
• For files that are utilities that export several functions/classes use the UpperCamelCase version ie: DateUtils.
• HOCs should be named in camelCase like withOnyx.
• All React components should be PascalCase (a.k.a. UpperCamelCase 🐫).

Platform-Specific File Extensions

In most cases, the code written for this repo should be platform-independent. In such cases, each module should have a single file, index.js, which defines the module's exports. There are, however, some cases in which a feature is intrinsically tied to the underlying platform. In such cases, the following file extensions can be used to export platform-specific code from a module:

• Mobile => index.native.js
• iOS/Android => index.ios.js/index.android.js
• Web => index.website.js
• Desktop => index.desktop.js

Note that index.js should be the default. i.e: If you have mobile-specific implementation in index.native.js, then the desktop/web implementation can be contained in a shared index.js. Furthermore, index.native.js should not be included in the same module as index.ios.js or index.android.js, nor should index.js be included in the same module as index.website.js or index.desktop.js.

API building

When adding new API commands (and preferably when starting using a new one that was not yet used in this codebase) always prefer to return the created/updated data in the command itself, instead of saving and reloading. ie: if we call CreateTransaction, we should prefer making CreateTransaction return the data it just created instead of calling CreateTransaction then Get rvl=transactionList

Storage Eviction

Different platforms come with varying storage capacities and Onyx has a way to gracefully fail when those storage limits are encountered. When Onyx fails to set or modify a key the following steps are taken:

1. Onyx looks at a list of recently accessed keys (access is defined as subscribed to or modified) and locates the key that was least recently accessed
2. It then deletes this key and retries the original operation

By default, Onyx will not evict anything from storage and will presume all keys are "unsafe" to remove unless explicitly told otherwise.

To flag a key as safe for removal:

• Add the key to the safeEvictionKeys option in Onyx.init(options)
• Implement canEvict in the Onyx config for each component subscribing to a key
• The key will only be deleted when all subscribers return true for canEvict

e.g.

Onyx.init({
    safeEvictionKeys: [ONYXKEYS.COLLECTION.REPORT_ACTIONS],
});

export default withOnyx({
    reportActions: {
        key: ({reportID}) => `${ONYXKEYS.COLLECTION.REPORT_ACTIONS}${reportID}`,
        canEvict: props => !props.isActiveReport,
    },
})(ReportActionsView);

Things to know or brush up on before jumping into the code

1. The major difference between React-Native and React are the components that are used in the render() method. Everything else is exactly the same. If you learn React, you've already learned 98% of React-Native.
2. The application uses React-Router for navigating between parts of the app.
3. Higher Order Components are used to connect React components to persistent storage via Onyx.

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Philosophy

This application is built with the following principles.

1. Data Flow - Ideally, this is how data flows through the app:

   1. Server pushes data to the disk of any client (Server -> Pusher event -> Action listening to pusher event -> Onyx). Currently the code only does this with report comments. Until we make more server changes, this steps is actually done by the client requesting data from the server via XHR and then storing the response in Onyx.
   2. Disk pushes data to the UI (Onyx -> withOnyx()/connect() -> React component).
   3. UI pushes data to people's brains (React component -> device screen).
   4. Brain pushes data into UI inputs (Device input -> React component).
   5. UI inputs push data to the server (React component -> Action -> XHR to server).
   6. Go to 1

2. Offline first

   • All data that is brought into the app and is necessary to display the app when offline should be stored on disk in persistent storage (eg. localStorage on browser platforms). AsyncStorage is a cross-platform abstraction layer that is used to access persistent storage.
   • All data that is displayed, comes from persistent storage.

3. UI Binds to data on disk

   • Onyx is a Pub/Sub library to connect the application to the data stored on disk.
   • UI components subscribe to Onyx (using withOnyx()) and any change to the Onyx data is published to the component by calling setState() with the changed data.
   • Libraries subscribe to Onyx (with Onyx.connect()) and any change to the Onyx data is published to the callback with the changed data.
   • The UI should never call any Onyx methods except for Onyx.connect(). That is the job of Actions (see next section).
   • The UI always triggers an Action when something needs to happen (eg. a person inputs data, the UI triggers an Action with this data).
   • The UI should be as flexible as possible when it comes to:
     • Incomplete or missing data. Always assume data is incomplete or not there. For example, when a comment is pushed to the client from a pusher event, it's possible that Onyx does not have data for that report yet. That's OK. A partial report object is added to Onyx for the report key report_1234 = {reportID: 1234, isUnread: true}. Then there is code that monitors Onyx for reports with incomplete data, and calls fetchChatReportsByIDs(1234) to get the full data for that report. The UI should be able to gracefully handle the report object not being complete. In this example, the sidebar wouldn't display any report that doesn't have a report name.
     • The order that actions are done in. All actions should be done in parallel instead of sequence.
       • Parallel actions are asynchronous methods that don't return promises. Any number of these actions can be called at one time and it doesn't matter what order they happen in or when they complete.
       • In-Sequence actions are asynchronous methods that return promises. This is necessary when one asynchronous method depends on the results from a previous asynchronous method. Example: Making an XHR to command=CreateChatReport which returns a reportID which is used to call command=Get&rvl=reportStuff.

4. Actions manage Onyx Data

   • When data needs to be written to or read from the server, this is done through Actions only.
   • Public action methods should never return anything (not data or a promise). This is done to ensure that action methods can be called in parallel with no dependency on other methods (see discussion above).
   • Actions should favor using Onyx.merge() over Onyx.set() so that other values in an object aren't completely overwritten.
   • In general, the operations that happen inside an action should be done in parallel and not in sequence (eg. don't use the promise of one Onyx method to trigger a second Onyx method). Onyx is built so that every operation is done in parallel and it doesn't matter what order they finish in. XHRs on the other hand need to be handled in sequence with promise chains in order to access and act upon the response.
   • If an Action needs to access data stored on disk, use a local variable and Onyx.connect()
   • Data should be optimistically stored on disk whenever possible without waiting for a server response. Example of creating a new optimistic comment:
     1. user adds a comment
     2. comment is shown in the UI (by mocking the expected response from the server)
     3. comment is created in the server
     4. server responds
     5. UI updates with data from the server

5. Cross Platform 99.9999%

   1. A feature isn't done until it works on all platforms. Accordingly, don't even bother writing a platform-specific code block because you're just going to need to undo it.
   2. If the reason you can't write cross platform code is because there is a bug in ReactNative that is preventing it from working, the correct action is to fix RN and submit a PR upstream -- not to hack around RN bugs with platform-specific code paths.
   3. If there is a feature that simply doesn't exist on all platforms and thus doesn't exist in RN, rather than doing if (platform=iOS) { }, instead write a "shim" library that is implemented with NOOPs on the other platforms. For example, rather than injecting platform-specific multi-tab code (which can only work on browsers, because it's the only platform with multiple tabs), write a TabManager class that just is NOOP for non-browser platforms. This encapsulates the platform-specific code into a platform library, rather than sprinkling through the business logic.
   4. Put all platform specific code in dedicated files and folders, like /platform, and reject any PR that attempts to put platform-specific code anywhere else. This maintains a strict separation between business logic and platform code.

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Deploying

Continuous deployment / GitHub workflows

Every PR merged into main will kick off the Create a new version GitHub workflow defined in .github/workflows/version.yml. It will look at the current version and increment it by one build version (using react-native-version), create a PR with that new version, and tag the version.

The PR will be merged automatically by the GitHub workflow automerge to keep the version always up to date.

When a new tag is pushed, it will trigger a deploy of all four clients:

1. The web app automatically deploys via a GitHub Action in .github/workflows/main.yml
2. The MacOS desktop app automatically deploys via a GitHub Action in .github/workflows/desktop.yml
3. The Android app automatically deploys via a GitHub Action in .github/workflows/android.yml
4. The iOS app automatically deploys via a GitHub Action in .github/workflows/ios.yml

Local production build

Sometimes it might be beneficial to generate a local production version instead of testing on production. Follow the steps below for each client:

Local production build of the web app

In order to generate a production web build, run npm run build, this will generate a production javascript build in the dist/ folder.

Local production build of the MacOS desktop app

In order to compile a production desktop build, run npm run desktop-build, this will generate a production app in the dist/Mac folder named Chat.app.

Local production build the iOS app

In order to compile a production iOS build, run npm run ios-build, this will generate a Chat.ipa in the root directory of this project.

Local production build the Android app

To build an APK to share run (e.g. via Slack), run npm run android-build, this will generate a new APK in the android/app folder.