Bundler CommonJS Import Limit and Circular Dependency Behavior in Bun

Goal

Diagnose a failed deployment that stops at build time when Bun’s bundler encounters a CommonJS module or a circular ES module dependency.

Constraints

• Bun’s bundler accepts only ES modules; attempting to import a CommonJS module (e.g., require('fs')) during bun build triggers a compile‑time error.
• Dynamic imports must use a literal string; import(moduleName) where moduleName is a variable is not resolved.
• Circular ES module dependencies are resolved by the bundler, but the execution order may differ from Node’s runtime, and this behavior is not fully documented.

Unresolved Questions

1. Does Bun’s bundler guarantee the same execution order for circular ES module dependencies as Node does at runtime, or can the order differ in a way that breaks application logic?
2. What is the recommended approach to detect and mitigate bundler failures caused by importing CommonJS modules during the build process?
3. Is there an upcoming flag or feature that will allow dynamic imports with variable expressions, or is this limitation permanent?