# Setting up debug environment

Once you have set up a `launch.json` file with default configurations, you can modify these configurations, or add new ones to the list. You can use other fields in these configurations as well.

![React Native launch configuration file](../images/launch-config.png)

For example, you can modify the `target` field to specify the simulator you want to target for iOS debugging or the device using the one from output of `adb devices` command for Android debugging.

## Debugging with TypeScript and Haul

If you use Haul instead of the react-native packager, you must add `sourceMapPathOverrides` to the `launch.json` file.

For example:
```
"sourceMapPathOverrides": {
    "webpack:///./~/*":   "${workspaceRoot}/node_modules/*",
    "webpack:///./*":   "${workspaceRoot}/*",
    "webpack:///*":     "*"
}
```
See more about source map overrides [here](https://github.com/Microsoft/vscode-node-debug2#sourcemappathoverrides)

## Specifying scheme for iOS app

If you want to use custom scheme for your application you can either pass it as part of `runArguments` parameter arguments or set `scheme` configuration parameter as shown below:
```js
"runArguments": ["--scheme", "customScheme", ...]
// or
"runArguments": ["--scheme=customScheme", ...]
// or
"scheme" : "customScheme"
```
Please be aware, specifying scheme value as a part of `runArguments` parameter arguments will override `scheme` configuration parameter value if it set.

## Debugging on iOS device

Debugging on an iOS device require following manual steps:
* Install [ios-deploy](https://www.npmjs.com/package/ios-deploy) `npm install -g ios-deploy`.
* Have a valid iOS Development certificate installed.
* In your project's `launch.json` file set `target` to `device` or use 'launchArguments' property to specify particular device to run on in case of multiple devices connected, e.g. `"runArguments": [ "--device", "My iPhone" ]`
* Choose **Debug iOS** configuration from the Configuration dropdown and press F5.
* Shake the device to open the development menu and select "Debug JS Remotely".

## Debugging React Native Windows

For UWP apps use `windows` target platform in `launch.json` configuration, e.g.:

```
{
    "name": "Debug UWP",
    "cwd": "${workspaceFolder}",
    "type": "reactnative",
    "request": "launch",
    "platform": "windows"
}
```

For WPF apps use `wpf`, e.g.(WPF debugging available only for react-native-windows gt 0.55.0):

```
{
    "name": "Debug WPF",
    "cwd": "${workspaceFolder}",
    "type": "reactnative",
    "request": "launch",
    "platform": "wpf"
}
```

## Debugging React Native apps with Hermes enabled

Hermes is the new JavaScript engine optimized for running React Native apps on Android. It improves app performance and decreases app size.

Click [here](https://facebook.github.io/react-native/docs/hermes/) to learn more about Hermes.

Debugging apps with Hermes enabled is currently experimental. Please, see [this issue](https://github.com/microsoft/vscode-react-native/issues/1073) for current known issues on Hermes support.

To debug while using Hermes engine, please choose one of the following debug configurations:
 - React Native (Hermes): Debug Android - Experimental

```
{
    "name": "Debug Android (Hermes) - Experimental",
    "cwd": "${workspaceFolder}",
    "type": "reactnativedirect",
    "request": "launch",
    "platform": "android"
}
```

 - React Native (Hermes): Attach to Hermes application - Experimental

 ```
{
    "name": "Attach to Hermes application - Experimental",
    "cwd": "${workspaceFolder}",
    "type": "reactnativedirect",
    "request": "attach"
}
```