dce-edge

Use this skill when changing conditional require() paths, Node-only imports, or edge/runtime branching. Webpack only DCEs a require() when it sits inside the dead branch of an if/else whose condition DefinePlugin can evaluate at compile time. What does NOT work: Always test edge changes with pnpm test-start-webpack on test/e2e/app-dir/app/standalone.test.ts (has edge routes), not with NEXT_SKIP_ISOLATE=1 which skips the full webpack compilation. Use if/else (not two independent if blocks) when assigning a variable conditionally on process.env.X . TypeScript cannot prove exhaustiveness across if (flag) { x = a }; if (!flag) { x = b } and will error with "variable used before being assigned". The if/else pattern satisfies both TypeScript (definite assignment) and webpack DCE. Platform-specific code (node vs web) can use a single .ts switcher module that conditionally require() s either .node.ts or .web.ts into a typed variable, then re-exports the shared runtime API as named exports. Keep the branch as if/else so DefinePlugin can dead-code-eliminate the unused require() .