Debugging multiple MiniApps

This guide present a Visual Studio Code setup to debug multiple MiniApps with the help of ern start command.

Prerequisites

Visual Studio Code should be installed, as well as the React Native Tools extension.

Setup

To make the setup easier to understand, let's illustrate it with an example.

Let's assume that we are working on an application that contains three different MiniApps (MiniAppA / MiniAppB and MiniAppC). We'd like to be able to run the native application and debug MiniAppA and MiniAppC in Visual Studio Code. We don't really care about being able to debug MiniAppB as we are not actively involved in its development. Also, let's assume that the package names of these MiniApps (as seen in name field of their package.json) are miniapp-a, miniapp-b, miniapp-c.

Given this, here is what we will do :

• Create a directory that will contain all the MiniApps that we need to debug in VSCode. Let's name this directory ern-workspace for example

$ mkdir ern-workspace

• Git clone (in this directory) all the MiniApps that we'd like to be able to debug, in our case MiniAppA and MiniAppB.

At this point we now have the following directory structure

ern-workspace
├── MiniAppA
└── MiniAppC

• Create a node project in this directory, and add react-native dependency to it

This is necessary for the React Native Tools extension to properly work.

We will use yarn for this, but feel free to use npm, it does not really matter.

$ yarn init . --yes
$ yarn add react-native@0.60.5

Make sure to install the react-native version that is being used by the MiniApps (in this current scenario our MiniApps are using React Native 0.60.5).

Our directory structure should now look like this

ern-workspace
├── MiniAppA
├── MiniAppC
├── node_modules
├── package.json
└── yarn.lock

• Create a Visual Studio Code debug configuration

This configuration will be used to attach the Visual Studio Code debugger (actually the React Native Tools debug adapter) to the native application.

We will create a new file ern-workspace/.vscode/launch.json with the following content:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Attach to packager",
            "cwd": "${workspaceFolder}",
            "type": "reactnative",
            "request": "attach",
            "sourceMapPathOverrides": {
                "../../composite/node_modules/miniapp-a/*": "${workspaceFolder}/MiniAppA/*",
                "../../composite/node_modules/miniapp-c/*": "${workspaceFolder}/MiniAppC/*"
            }
        }
    ]
}

Note that in the sourceMapPathOverrides, the MiniApp package names are used, and could differ from the name of the directory (name of the repo) that contains the source code of the MiniApp (in our case it is different indeed. For example MiniAppA package name is miniapp-a). If a MiniApp is using a scoped package name, make sure to include the scope as well in the path.

There should be one line per MiniApp in sourceMapPathOverrides configuration and it should always be formatted as follow :

"../../composite/node_modules/[MINIAPP_PACKAGE_NAME]/*": "${workspaceFolder}/[MINIAPP_DIRECTORY_NAME]/*"

[MINIAPP_PACKAGE_NAME] should be the package name of the MiniApp (for ex miniapp-a or @company/cool-miniapp for example) [MINIAPP_DIRECTORY_NAME] should be the associated directory name where the MiniApp has be cloned to in ern-workspace (for ex MiniAppA)

At this point our directory structure should be

ern-workspace
├── .vscode
│   └── launch.json
├── MiniAppA
├── MiniAppC
├── node_modules
├── package.json
└── yarn.lock

The basic setup is now complete. If you need to add more MiniApps over time, just clone any additional MiniApps in the ern-workspace directory and make sure to add a corresponding mapping entry to sourceMapPathOverrides configuration.

We can now start debugging with the help of the ern start command.

Debbuging

You can now use ern start command as you are used to. The only thing that is required for this setup to work is for the Electrode Native Composite (generated as part of ern start command execution) to be generated in the composite directory in our ern-workspace directory. Assuming that the absolute path to ern-workspace directory is /path/to/ern-workspace, we can just use the --compositeDir option of ern start to achieve this, as follow :

$ ern start [options] --compositeDir /path/to/ern-workspace/composite

[options] are any other options that you might be using for ern start command, for example the MiniApps to include in the composite, or a cauldron descriptor to retrieve MiniApps from.

Once commnand execution is done, our final directory structure should look like :

ern-workspace
├── .vscode
│   └── launch.json
├── composite
├── MiniAppA
├── MiniAppC
├── node_modules
├── package.json
└── yarn.lock

You can now open the ern-workspace directory in Visual Studio Code (if not done already) and launch the native application (if it is not already launched or is not being launched automatically by ern start if you have a binary store configured).

To attach Visual Studio Code to the React Native debugger (first make sure that ern start command has completed and is still running in the background -i.e not killed-), you should run the Attach to packager debug configuration from Visual Studio Code. You will notice an indicator that will keep spinning until Visual Studio Code gets attached to the React Native debugger.

In the native application, bring up the React Native Developer Menu, and turn on JS Debugging by tapping the Debug JS Remotely button. This will result in attaching to the Visual Studio Code debugger (if debugging was already turned on in the native app, just retrigger the debugger by tapping Stop Remote JS Debugging and then Debug JS Remotely). In Visual Studio Code you should now see that the debugger was attached, and you should see the visual studio icons part of a debbugging session. We are now able to put breakpoints in MiniAppA and MiniAppC sources, and debug the MiniApps from Visual Studio Code.

You will notice that if you are doing code changes in MiniAppA and MiniAppC directories, the changes won't be picked up by React Native even if you reload the app. If you need to perform modifications on the MiniApps, you will have to use the ern link command. For example if you need to perform code changes for MiniAppA, you can just run ern link from MiniAppA directory (this is a one time operation only -once per MiniApp being linked- and you'll need to relaunch ern start any time you link a new MiniApp).