Describe the bug

When NODE_ENV=production is set in the shell environment, slidev (dev server) renders a completely blank white page. The JavaScript console shows: ReferenceError: __DEV__ is not defined.

Root cause: @slidev/client/env.ts uses export const mode = __DEV__ ? 'dev' : 'build', but __DEV__ is not a standard Vite variable — it was auto-defined by older Vite versions via a Vue compatibility shim, and Vite 8 no longer guarantees it. When NODE_ENV=production is present, Vite 8's import.meta.env.DEV reports false even in dev server mode, and the __DEV__ define (which Slidev's getDefine() correctly maps to options.mode === "dev") doesn't take effect.

The fix is a one-line change: replace __DEV__ with Vite's standard import.meta.env.DEV, which correctly reflects the Vite mode regardless of NODE_ENV.

Minimal reproduction

Steps to reproduce:

1. export NODE_ENV=production
2. pnpm create slidev (or npm create slidev@latest) — Slidev v52.17.0
3. pnpm run dev
4. Open http://localhost:3030 → completely blank page
5. Check console: ReferenceError: __DEV__ is not defined

You can use https://sli.dev/new to create a new project.

This is reproducible whenever NODE_ENV=production is present — common in CI/CD environments, Docker containers, or developer machines with global NODE_ENV set.

Proposed fix

In @slidev/client/env.ts, line 5:

- export const mode = __DEV__ ? 'dev' : 'build'
+ export const mode = import.meta.env.DEV ? 'dev' : 'build'

import.meta.env.DEV is the standard Vite API for detecting dev mode. It correctly reports true in dev server and false in production builds, and is NOT affected by NODE_ENV. This fix:

• ✅ Fixes the bug when NODE_ENV=production
• ✅ No change in behavior when NODE_ENV is unset or development
• ✅ No change in production build behavior (import.meta.env.DEV is false at build time)
• ✅ Eliminates dependency on the non-standard __DEV__ global

Workaround (until fixed)

// package.json
"dev": "NODE_ENV=development slidev"

Environment

• Slidev version: 52.17.0
• Node: v26.2.0
• pnpm: v11.11.0
• OS: macOS 26.5.2

Additional context

Related to closed issue #2142 (same error, closed without root cause analysis — the reporter likely had NODE_ENV=production set without realizing it).