Does React Native compile JavaScript into Java for Android?

When I develop hybrid apps with React Native. Does the JavaScript code I write transform into Java-Code or Java-Bytecode for the Dalvik/ART Runtime when I create an Android-App from my React Native code? Or are just the UI components compiled into native UI components? Or does a library like the Fetch API compile the JavaScript code into Java-Code or Java-Bytecode?

Basically, you write Javascript. The Javascript communicates with native components (Java on Android, Objective C on iOS, C# on Windows).

The communication occurs through the so-called "bridge". If at any time you feel that this communication slows things down too much, you can choose to implement the Javascript functionality in Java, Objective C, or C# respectively in order to run purely native. In this case, you are writing directly in native code, so there's no Javascript to native compilation.

This will sacrifice compatibility for performance. Normally, this is not necessary.

• Further reading

Understanding React Native bridge concept

The code remains the JavaScript native code and is not converted into any other format. The hybrid apps run inside the native container app which invokes JavaScript run time engine which takes care of executing the JavaScript code. I hope this clarifies the question.