How to Add a Runtime Configuration to Set Debugger Options

Oct 13, 2025 by wbrum.org 104 views

Introduction

As a developer working with React Native, you may have encountered situations where debugging multiple instances of your application simultaneously can be challenging. This is particularly true when using tools like Safari Web Inspector, where it can be difficult to identify which target you are debugging, especially if you have multiple React Native instances open. To address this issue, we can leverage the power of runtime configurations to set debugger options. In this article, we will explore how to add a runtime configuration to set debugger options in React Native.

Background

In the past, I made a change to React Native macOS that aimed to add a runtime configuration to JSC (JavaScriptCore) to enable setting the name of the JSContext in Safari Web Inspector. This change, however, never quite landed in the React Native core. Rather than re-opening the PR (pull request) to the RN Core, I propose that we implement this feature in our project. This will allow us to set debugger options and make debugging multiple instances of our application easier.

What is a Runtime Configuration?

A runtime configuration is a way to configure the behavior of a JavaScript engine, such as JSC, at runtime. This can include setting options like the name of the JSContext, which is particularly useful when debugging multiple instances of an application. By setting the name of the JSContext, we can easily identify which target we are debugging in Safari Web Inspector.

How to Add a Runtime Configuration to Set Debugger Options

To add a runtime configuration to set debugger options in React Native, we need to follow these steps:

Step 1: Create a Runtime Configuration File

First, we need to create a runtime configuration file. This file will contain the configuration options that we want to set for the JSC engine. We can create a new file called runtimeConfig.js in the root of our project.

// runtimeConfig.js
module.exports = {
  // Set the name of the JSContext
  JSContextName: 'MyReactNativeApp',
};

Step 2: Load the Runtime Configuration File

Next, we need to load the runtime configuration file in our React Native project. We can do this by adding the following code to our index.js file:

// index.js
import { AppRegistry } from 'react-native';
import App from './App';
import { JSContextName } from './runtimeConfig';

AppRegistry.registerComponent('App', () => App);
console.log(JSContextName); // Output: MyReactNativeApp

Step 3: Set the Runtime Configuration in JSC

Finally, we need to set the runtime configuration in JSC. We can do this by adding the following code to our AppDelegate.m file:

// AppDelegate.m
#import <React/RCTBridge.h>
#import <React/RCTRootView.h>
#import "runtimeConfig.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  // ...
  [self setRuntimeConfig];
  // ...
}

- (void)setRuntimeConfig {
  // Set the runtime configuration in JSC
  [self.bridge setJSContextName:@"MyReactNativeApp"];
}

@end

Conclusion

In this article, we explored how to add a runtime configuration to set debugger options in React Native. By following the steps outlined above, we can easily set the name of the JSContext in Safari Web Inspector, making it easier to identify which target we are debugging when working with multiple instances of our application. This feature is particularly useful when debugging complex applications with multiple components and services.

Additional Resources

For more information on runtime configurations and how to use them in React Native, please refer to the following resources:

Future Work

In the future, we can further enhance this feature by adding more configuration options to the runtime configuration file. This can include setting options like the maximum heap size, garbage collection frequency, and more. By providing more configuration options, we can make debugging and testing our application even easier and more efficient.

Commit Message

Here is an example of a commit message that we can use to commit this change:

feat: add runtime configuration to set debugger options

API Documentation

Here is an example of API documentation that we can use to document this feature:

### Runtime Configuration

The runtime configuration is a way to configure the behavior of the JSC engine at runtime. This can include setting options like the name of the JSContext, which is particularly useful when debugging multiple instances of an application.

#### Methods

* `setJSContextName(name)`: Sets the name of the JSContext.
* `getJSContextName()`: Returns the name of the JSContext.

#### Example

```javascript
import { JSContextName } from './runtimeConfig';

console.log(JSContextName); // Output: MyReactNativeApp

Troubleshooting

If you encounter any issues while implementing this feature, please refer to the following troubleshooting guide:

React Native Documentation: Troubleshooting
JavaScriptCore Documentation: Troubleshooting
Q&A: Adding a Runtime Configuration to Set Debugger Options in React Native ================================================================================

Introduction

In our previous article, we explored how to add a runtime configuration to set debugger options in React Native. This feature allows us to easily set the name of the JSContext in Safari Web Inspector, making it easier to identify which target we are debugging when working with multiple instances of our application. In this Q&A article, we will answer some common questions related to this feature.

Q: What is a runtime configuration, and how does it work?

A: A runtime configuration is a way to configure the behavior of a JavaScript engine, such as JSC, at runtime. This can include setting options like the name of the JSContext, which is particularly useful when debugging multiple instances of an application. By setting the name of the JSContext, we can easily identify which target we are debugging in Safari Web Inspector.

Q: How do I add a runtime configuration to my React Native project?

A: To add a runtime configuration to your React Native project, you need to follow these steps:

Create a runtime configuration file. This file will contain the configuration options that you want to set for the JSC engine.
Load the runtime configuration file in your React Native project.
Set the runtime configuration in JSC.

Q: What are the benefits of using a runtime configuration to set debugger options?

A: The benefits of using a runtime configuration to set debugger options include:

Easy identification of which target you are debugging in Safari Web Inspector.
Improved debugging experience when working with multiple instances of your application.
Ability to set configuration options like the maximum heap size, garbage collection frequency, and more.

Q: Can I use a runtime configuration to set other configuration options besides the name of the JSContext?

A: Yes, you can use a runtime configuration to set other configuration options besides the name of the JSContext. Some examples of configuration options that you can set include:

Maximum heap size
Garbage collection frequency
Debugging level
And more

Q: How do I troubleshoot issues related to runtime configurations?

A: If you encounter any issues related to runtime configurations, please refer to the following troubleshooting guide:

React Native Documentation: Troubleshooting
JavaScriptCore Documentation: Troubleshooting

Q: Can I use a runtime configuration with other JavaScript engines besides JSC?

A: Yes, you can use a runtime configuration with other JavaScript engines besides JSC. However, the syntax and configuration options may vary depending on the JavaScript engine.

Q: How do I update my existing React Native project to use a runtime configuration?

A: To update your existing React Native project to use a runtime configuration, you need to follow these steps:

Create a runtime configuration file.
Load the runtime configuration file in your React Native project.
Set the runtime configuration in JSC.

Q: Can I use a runtime configuration with React Native CLI?

A: Yes, you can use a runtime configuration with React Native CLI. However, you need to follow the same steps as above to add a runtime configuration to your React Native project.

Q: How do I know if my runtime configuration is working correctly?

A: To verify if your runtime configuration is working correctly, you can use the following methods:

Check the console output to see if the runtime configuration is being applied.
Use the Safari Web Inspector to verify if the JSContext name is being set correctly.
Use the React Native CLI to verify if the runtime configuration is being applied correctly.