Synchronous TurboModules in React Native Can Silently Block the JS Thread

React Native's New Architecture enables synchronous communication between JavaScript and native code via TurboModules, but this comes with a hidden performance risk. A synchronous native call forces the JavaScript thread to wait until the native operation completes, regardless of how fast the communication layer itself is. Operations like Keystore access, decryption, disk reads, or JSON parsing can introduce variable latency that blocks all other JS work, including renders and user interaction handling. Calling such methods repeatedly inside component render cycles can cause UI freezes, dropped animation frames, and sluggish navigation, especially on lower-end devices. TurboModules improve the communication overhead over the older bridge, but they do not eliminate the cost of the underlying native work itself.