Summary

In this chapter, we had a look at JavaScript engines in general, learned about the special requirements React Native has for a JavaScript engine, the different engines we can use in React Native, and how to change the JS engine of our React Native project. We then had a look at Hermes, a JavaScript engine developed with mobile in general and React Native especially in mind.

After understanding the approach of Hermes and its benefits, we compared mobile app key metrics on apps running on JavaScriptCore, V8, and Hermes. While there is no big difference in using JSC or V8, Hermes brings a huge boost in terms of TTI and memory utilization to React Native.

After mastering JavaScript engines, we’ll have a look at useful tools when working with React Native in the next chapter.