Hermes engine in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Hermes engine in React Native?

Hermes is a JavaScript engine optimized for running React Native apps on Android and iOS. It improves app start time, reduces memory usage, and enhances overall performance.

intermediate

How does Hermes improve app startup time?

Hermes compiles JavaScript into bytecode ahead of time, so the app can start faster by skipping the usual JavaScript parsing and compilation during launch.

beginner

Which platforms support Hermes in React Native?

Hermes supports Android and iOS platforms for React Native apps, helping improve performance on both mobile operating systems.

intermediate

How do you enable Hermes in a React Native project?

To enable Hermes, you update the React Native configuration files (like android/app/build.gradle for Android and Podfile for iOS) to turn Hermes on, then rebuild the app.

advanced

What are some trade-offs when using Hermes?

While Hermes improves startup and memory, it may have limited support for some JavaScript features and debugging tools compared to other engines like JavaScriptCore.

What is the main benefit of using Hermes in React Native?

A Built-in database support

B Better UI design tools

C Automatic code generation

D Faster app startup and lower memory use

Hermes is designed to improve app startup speed and reduce memory consumption.

Which platforms can run React Native apps with Hermes?

A Only Android

B Only iOS

C Android and iOS

D Windows and Linux

Hermes supports both Android and iOS platforms.

How does Hermes improve performance?

A By compiling JavaScript to bytecode ahead of time

B By using more CPU cores

C By caching images automatically

D By reducing app size only

Hermes compiles JavaScript into bytecode before running, speeding up app launch.

What must you do to use Hermes in your React Native app?

A Enable Hermes in build configuration and rebuild the app

B Install a separate Hermes app

C Write JavaScript in a special Hermes syntax

D Use a different programming language

Hermes is enabled by changing build settings and rebuilding the app.

What is a possible downside of using Hermes?

A Slower app startup

B Limited support for some JavaScript features

C Increased app size

D No support for Android

Hermes may not support all JavaScript features or debugging tools fully.

Explain what Hermes engine is and why it is used in React Native apps.

Think about how apps start and run faster with Hermes.

Describe the steps to enable Hermes in a React Native project.

Focus on what files you change and what you do after.