esbuild 0.21 vs SWC 1.5 vs Babel 8: Transpiling TypeScript 5.6 Showdown

TypeScript 5.6 introduces long-awaited features like stable decorators, const type parameters, and improved narrowing, but transpiling this code requires build tools that keep pace. We pit three popular transpilers against each other: esbuild 0.21, SWC 1.5, and the upcoming Babel 8, to see which delivers the best balance of speed, output quality, and compatibility.

Test Setup and Methodology

We used a 12,000-line real-world TypeScript codebase with heavy use of TypeScript 5.6-exclusive features: stage 3 decorators, const type parameters, satisfies operator edge cases, and new Array.prototype methods.…