Runtime Error: Writing JS Libraries in the Age of Fragmentation
🌲 Join us at CascadiaJS 2027! https://luma.com/cascadiajs-2027
Recorded live at CascadiaJS 2025 in Seattle.
Speaker: Dominic Kundel
Building for the web used to mean fighting browser quirks. Now, it's runtime quirks. Node.js, Deno, Bun, Cloudflare Workers, Edge runtimes, React Native, they all run JavaScript, sort of. Each comes with its own gotchas.
Throw in ESM vs CJS, native TypeScript vs compiled JS, export maps, bundlers, and half-supported compatibility layers, and you’ve got a new kind of chaos.
In this talk, I’ll share the challenges we faced building the OpenAI Agents SDK and how we navigated the messy modern JS landscape.
00:00 From Internet Explorer Hacks to Modern Runtimes
01:12 The New Challenge for JavaScript Library Authors
01:57 Building the OpenAI Agents SDK Everywhere
03:00 Async Local Storage and Runtime Compatibility
04:20 Why Cloudflare Workers Are Different
04:44 Bundling vs Conditional Imports
05:18 Export Maps and Conditional Exports
06:15 Bundlers, Edge Cases, and Runtime Quirks
07:35 Building a Cross-Runtime Test Suite
08:28 The New Era of Runtime Fragmentation
08:50 Practical Advice for Library Authors
Watch more CascadiaJS 2025 talks:
• CascadiaJS 2025 Recap