React Native is an offshoot of React, a Facebook-built JavaScript framework released two years ago for building mobile app user interfaces with HTML5 and other Web standards.

Cross-platform frameworks—tools like React Native and Flutter—let you write one codebase for both iOS and Android. They’re designed to cut duplication, speed up work and unify teams.

Flutter emerged a bit later (first teased in 2015, released around 2017) from Google’s labs. It came with its own engine, ...