Fix Vite build errors

Most Vite errors trace to one of four causes: env vars read the old way, CommonJS-to-ESM interop, dependency pre-bundling, or production Rollup behavior that differs from the dev server. Diagnose by which phase fails.

WorkflowDifficulty: moderatelow risk

Last verified May 20, 2026 · Updated May 22, 2026

Vite errors usually fall into four buckets: import.meta.env reads returning undefined, CommonJS interop ('does not provide an export named default'), dependency pre-bundling needing optimizeDeps, and production Rollup builds behaving differently from the dev server. Identify the failing phase first — dev server vs production build — then match the bucket.

Symptoms

'does not provide an export named default' when importing a CommonJS package.
import.meta.env.VITE_X is undefined at runtime.
Works in `vite` dev but fails in `vite build` (or vice versa).
SSR errors about an externalized dependency.

Likely causes

Default-vs-named import mismatch against a CommonJS module's interop shape.
An env var missing the VITE_ prefix, so it is not exposed to client code.
A CommonJS dependency that needs to be force pre-bundled via optimizeDeps.include.
ssr.noExternal not set for a package that must be bundled for the server build.
Production-only Rollup tree-shaking or resolution that the dev server skips.

Error to fix

Error	Likely cause	Fix
no export named 'default'	CommonJS interop	Use a namespace/default import or add to optimizeDeps.include
import.meta.env.X undefined	Missing VITE_ prefix	Rename the env var to VITE_X and restart dev
Dev works, build fails	Rollup vs esbuild differences	Reproduce with `vite build` + `vite preview` and read the Rollup warning
SSR externalized error	ssr.noExternal not set	Add the package to ssr.noExternal

Diagnostic commands

shell

# Reproduce the production build (not just the dev server)$ npx vite build$ npx vite preview# Read the first Rollup warning's module path

Config fixes

optimizeDeps and SSR externalization

export default defineConfig({
  optimizeDeps: {
    // Force-prebundle a CommonJS dep that errors under native ESM.
    include: ['legacy-cjs-package'],
  },
  ssr: {
    // Bundle (don't externalize) a dep for the server build.
    noExternal: ['esm-only-package'],
  },
});

Test failure debuggingAI debugging prompt

I'm getting a Vite error: <paste the error and whether it happens in `vite` dev or `vite build`>. Identify which bucket it falls in — import.meta.env, CommonJS interop, optimizeDeps pre-bundling, or SSR externalization — then propose the smallest config or import change that fixes it. Prefer optimizeDeps.include / ssr.noExternal / an import-style fix over disabling features.

Safety: Do not disable the production build or broadly mark deps external to silence the error — fix the specific interop or env issue.

Safe fix workflow

Confirm which phase fails: dev server or production build.
For interop errors, fix the import style or add the package to optimizeDeps.include.
For env errors, rename the variable with a VITE_ prefix and restart the dev server.
For SSR errors, add the package to ssr.noExternal.
Re-run `vite build` + `vite preview` to confirm the production path is clean.

Escalation checklist

The error reproduces only in the production build, not in dev
A dependency ships no ESM build and resists optimizeDeps
The interop error comes from a transitive dependency you do not control

Official sources

Official docsVite Guidevitejs.devreliability 98%
Backs the breaking-change and migration-step claims.
GitHub releasevitejs/vite releasesvitejs/vitereliability 92%
Backs the breaking-change and migration-step claims.