Invariant violation: calling synchronous methods on native modules is not supported in chrome.

The error “invariant violation: calling synchronous methods on native modules is not supported in chrome” typically occurs when using synchronous methods on native modules while developing applications using React Native.

In React Native, native modules are used to bridge JavaScript code with platform-specific code. Native modules often handle operations that require asynchronous behavior, such as accessing device features or performing network requests. Asynchronous operations are preferred in React Native to prevent blocking the main UI thread.

To illustrate the issue, let’s assume you have a custom native module called “MyModule” which exposes a synchronous method named “getDataSync”. Here’s an example:

    public class MyModule extends ReactContextBaseJavaModule {
      // Module implementation...
      
      @ReactMethod
      public String getDataSync() {
        // Synchronous operation...
        return "Data";
      }
    }
  

In your JavaScript code, you may attempt to call this synchronous method like so:

    import { NativeModules } from 'react-native';
    
    const result = NativeModules.MyModule.getDataSync();
    console.log(result);
  

However, this approach will trigger the aforementioned invariant violation error in Chrome’s developer tools. This is because Chrome runs JavaScript code asynchronously, and calling synchronous native methods interrupts this asynchronous flow, leading to potential deadlocks or unresponsive UI.

To fix this error, it is recommended to restructure your code to use asynchronous methods, callbacks, or Promises in both the native module and the JavaScript code. Refactoring our previous example, we can modify the native module to include an asynchronous counterpart “getDataAsync”:

    public class MyModule extends ReactContextBaseJavaModule {
      // Module implementation...
      
      @ReactMethod
      public void getDataAsync(Callback callback) {
        // Asynchronous operation...
        String data = "Data";
        callback.invoke(data);
      }
    }
  

In JavaScript, you can now call the asynchronous method and handle the result using a callback or a Promise:

    import { NativeModules } from 'react-native';
    
    NativeModules.MyModule.getDataAsync((result) => {
      console.log(result);
    });
  

By following this asynchronous pattern, you avoid calling synchronous methods on native modules, ensuring that your React Native application remains responsive and runs smoothly.