How We Adopted TypeScript 5.6 for Our React 19 App and Reduced Runtime Errors by 90%

Introduction

Our team maintains a large-scale React 19 e-commerce application serving 500k+ monthly active users. For 18 months, we ran the app in plain JavaScript, relying on manual testing and sporadic ESLint rules to catch issues. Runtime errors—undefined property accesses, mismatched prop types, invalid state updates—plagued our sprint cycles, with an average of 42 runtime-related bugs reported per month. We knew we needed a type system, but waited for React 19’s stable release and TypeScript 5.6’s new features to align our migration timeline.

Why We Chose TypeScript 5.6 for React 19

TypeScript 5.6 shipped with several React-specific improvements that made it the ideal choice for our React 19 app:

Improved JSX type checking for React 19’s new use() hook and Server Components

Stricter nullish coalescing and optional chaining type inference, reducing accidental falsy value bugs

Faster project references and…