If you don't see the 'inspect' link, make sure the Metro server is running. You should now see a 'Hermes React Native' target with an 'inspect' link which can be used to bring up debugger. button to add the Metro server address (typically localhost:8081 as described above). Navigate to chrome://inspect in a Chrome browser instance. Once you know where the Metro server is listening, you can connect with Chrome using the following steps: When running yarn start the address is written to stdout on startup. Typically this will be on localhost:8081, but this is configurable. Note that this is very different with the 'Remote JS Debugging' from the In-App Developer Menu documented in the Debugging section, which actually runs the JS code on Chrome's V8 on your development machine (laptop or desktop).Ĭhrome connects to Hermes running on device via Metro, so you'll need to know where Metro is listening. If you've recently created a new app from scratch, you should see if Hermes is enabled in the welcome view:Ī HermesInternal global variable will be available in JavaScript that can be used to verify that Hermes is in use:

You can read more about the technical implementation on this page.

You can still disable Hermes using the command described in this page. This change is fully transparent to users of React Native. This fully eliminates this problem, and offers users a JS engine that is compatible with the specific React Native version. Historically, we had problems with matching versions of Hermes with versions of React Native. This will make sure you're consuming a version of Hermes which is fully compatible with the version of React Native you're using. We will be building a version of Hermes for you whenever we release a new version of React Native. React Native comes with a bundled version of Hermes. Hermes is used by default by React Native and no additional configuration is required to enable it. For many apps, using Hermes will result in improved start-up time, decreased memory usage, and smaller app size when compared to JavaScriptCore. Hermes is an open-source JavaScript engine optimized for React Native.

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