Setting the file. One moment.
Skill 03 · Vercel React Best Practices
Subchapter 3.16
rules/bundle-analyzable-paths.mdMarkdown2 KBView on GitHub
Build tools work best when import and file-system paths are obvious at build time. If you hide the real path inside a variable or compose it too dynamically, the tool either has to include a broad set of possible files, warn that it cannot analyze the import, or widen file tracing to stay safe.
Prefer explicit maps or literal paths so the set of reachable files stays narrow and predictable. This is the same rule whether you are choosing modules with import() or reading files in server/build code.
When analysis becomes too broad, the cost is real:
Incorrect (the bundler cannot tell what may be imported):
const PAGE_MODULES = {
home: './pages/home',
settings: './pages/settings',
} as const
const Page = await import(PAGE_MODULES[pageName])Correct (use an explicit map of allowed modules):
const PAGE_MODULES = {
home: () => import('./pages/home'),
settings: () => import('./pages/settings'),
} as const
const Page = await PAGE_MODULES[pageName]()Incorrect (a 2-value enum still hides the final path from static analysis):
const baseDir = path.join(process.cwd(), 'content/' + contentKind)Correct (make each final path literal at the callsite):
const baseDir =
kind === ContentKind.Blog
? path.join(process.cwd(), 'content/blog')
: path.join(process.cwd(), 'content/docs')In Next.js server code, this matters for output file tracing too. path.join(process.cwd(), someVar) can widen the traced file set because Next.js statically analyze import, require, and fs usage.
Reference: Next.js output (opens in a new tab), Next.js dynamic imports (opens in a new tab), Vite features (opens in a new tab), esbuild API (opens in a new tab), Rollup dynamic import vars (opens in a new tab), Webpack dependency management (opens in a new tab)