Fixing "Error: Unknown argument: prod" in Angular Build Commands

Problem Statement

If you're encountering the error "Error: Unknown argument: prod" when trying to build your Angular project with the command ng build --prod --aot, this is due to a significant change in the Angular CLI. The --prod flag, which was commonly used for production builds, has been deprecated and removed in recent Angular versions.

This error typically occurs when:

• You've updated your Angular project to version 12+ (deprecated) or 14+ (removed)
• You're using build scripts or CI/CD pipelines that still reference the old --prod flag
• Your development environment (ng serve) works correctly, but production builds fail

Solution

Use --configuration production Instead

The correct approach for Angular 12+ is to replace --prod with --configuration production:

ng build --configuration production --aot

Alternatively, you can use the shorthand version:

ng build -c production --aot

INFO

Since Angular 15, ng build without any configuration flags behaves identically to ng build --configuration production, making the explicit flag optional in many cases.

Update Package.json Scripts

If you have build scripts in your package.json file, update them to use the new syntax:

{
  "scripts": {
    "build": "ng build",
    "build-prod": "ng build --configuration production",
    "build:ssr": "ng build --configuration production && ng run app:server:production"
  }
}

After updating, you can run:

npm run build-prod

Update CI/CD Pipelines and Configuration Files

For projects integrated with .NET or other frameworks using build configuration files, you'll need to update these files:

Before (old syntax in .csproj files):

<Exec WorkingDirectory="$(SpaRoot)" Command="npm run build -- --prod" />
<Exec WorkingDirectory="$(SpaRoot)" Command="npm run build:ssr -- --prod" Condition=" '$(BuildServerSideRenderer)' == 'true' " />

After (new syntax):

<Exec WorkingDirectory="$(SpaRoot)" Command="npm run build -- --configuration production" />
<Exec WorkingDirectory="$(SpaRoot)" Command="npm run build:ssr -- --configuration production" Condition=" '$(BuildServerSideRenderer)' == 'true' " />

Background: Why This Change Occurred

The Angular team deprecated the --prod flag in Angular 12 and completely removed it in Angular 14 as part of their effort to streamline the CLI and align with more explicit configuration patterns. This change provides:

• Better consistency across different environments
• More flexibility for custom configurations
• Clearer syntax that explicitly indicates the configuration being used

WARNING

If you're working with multiple environments (development, staging, production), ensure your angular.json file contains the appropriate configuration definitions for each environment.

Verify Your Angular Version

To check which version of Angular you're using:

ng version

This will help you confirm whether your project has been updated to a version where --prod is no longer supported.

Alternative Solution for Legacy Projects

If you need to maintain compatibility with both old and new Angular versions temporarily, you can create custom scripts that check the Angular version and use the appropriate command:

#!/bin/bash
ANGULAR_VERSION=$(ng version | grep "Angular CLI" | awk '{print $3}')

if [[ $ANGULAR_VERSION == 1[2-9].* ]] || [[ $ANGULAR_VERSION == 2*.* ]]; then
    ng build --configuration production --aot
else
    ng build --prod --aot
fi

Conclusion

The "Unknown argument: prod" error is a straightforward fix that requires updating your build commands to use --configuration production instead of the deprecated --prod flag. This change affects not only your local development commands but also any CI/CD pipelines, deployment scripts, or configuration files that reference the old syntax.

By making these updates, you'll ensure your Angular projects build successfully across all current and future Angular versions while following the framework's recommended best practices.