Bridge

Also called Legacy bridge, React Native bridge

Part of
React Native Glossary
Also known as
Legacy bridge, React Native bridge
Related
JSILegacy vs New ArchitectureCommunication LayerNative Module
Mentioned in
Communication LayerExpoFabric RendererJSILegacy vs New Architecture
Updated

What is Bridge in React Native?

The bridge was React Native’s original asynchronous, JSON-serialised channel between JavaScript and native code. The New Architecture replaces it with JSI.

The bridge was the original mechanism connecting JavaScript to native code in React Native. Every interaction — mounting a view, calling a native module, delivering a touch event — was serialised to JSON, placed on a queue, and processed asynchronously on the other side.

That design bought thread safety and simplicity, but it had three well-known costs:

  • Serialisation overhead on every call, which grew with payload size.
  • No synchronous reads. JavaScript could never ask native code a question and get an immediate answer, which is why measuring a view was awkward.
  • Congestion. A busy queue — a fast scroll driving many events — meant frames arriving late.

The bridge is gone in bridgeless mode, the default since React Native 0.76, replaced by JSI.

Newcomers still meet the word constantly because a decade of blog posts, conference talks, and library READMEs describe React Native in bridge terms. If an article's central claim is "the bridge is the bottleneck", it predates late 2024.