iife with awaits in development only

[crabvk]

Describe the bug

I'm using iife as the build format. My code contains some awaits, but only inside

if (import.meta.env.DEV) {
  // Some `await`s are here.
}

Trying to build project with yarn run vite build -m production, getting error:

error during build:
Module format "iife" does not support top-level await. Use the "es" or "system" output formats rather.

Expected the code inside the if statement to be ignored in production build.

Reproduction

https://stackblitz.com/edit/vitejs-vite-hstwzwv1

Steps to reproduce

No response

System Info

System:
    OS: Linux 6.14 Artix Linux
    CPU: (16) x64 AMD Ryzen 7 5800X 8-Core Processor
    Memory: 24.55 GB / 31.25 GB
    Container: Yes
    Shell: 4.0.2 - /usr/bin/fish
  Binaries:
    Node: 22.16.0 - ~/.local/share/mise/installs/node/22.16.0/bin/node
    Yarn: 4.9.1 - ~/.npm-packages/bin/yarn
    npm: 10.9.2 - ~/.local/share/mise/installs/node/22.16.0/bin/npm
  Browsers:
    Chromium: 136.0.7103.113

Used Package Manager

yarn

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[github-actions]

Hello @crabvk. Please provide a minimal reproduction using a GitHub repository or StackBlitz. Issues marked with needs reproduction will be closed if they have no activity within 3 days.

[crabvk]

Minimal reproduction: https://stackblitz.com/edit/vitejs-vite-hstwzwv1

[github-actions]

Hello @crabvk. Please provide a minimal reproduction using a GitHub repository or StackBlitz. Issues marked with needs reproduction will be closed if they have no activity within 3 days.