DartDevCompiler (DDC)

The DartDevCompiler (DDC) is the development compiler for Dart web applications. It produces modular JavaScript output that supports fast incremental compilation during development.

Overview

DDC is the default compiler used by build_runner during development. It is optimized for fast edit-refresh cycles rather than production performance.

For production builds, use dart2js which produces optimized, minified output.

How It Works

DDC compiles each Dart library into a separate JavaScript module. This enables:

• Fast incremental compilation - Only recompile changed files
• Modular output - Each library is a separate module
• Source maps - Debug Dart code directly in the browser
• Hot reload - Fast development iteration

Configuration

DDC is configured through build.yaml:

targets:
  $default:
    builders:
      build_web_compilers|entrypoint:
        generate_for:
          - web/main.dart
        options:
          compiler: dartdevc

Development Server

Use build_runner serve for development:

dart run build_runner serve

This starts a development server with:

• DDC compilation
• Incremental rebuilds on file changes
• Live reload in the browser

Production Builds

For production, switch to dart2js:

dart run build_runner build --release

Or configure in build.yaml:

targets:
  $default:
    builders:
      build_web_compilers|entrypoint:
        options:
          compiler: dart2js
          dart2js_args:
            - -O4
            - --minify

Differences from dart2js

Feature	DDC	dart2js
Compilation speed	Fast	Slow
Output size	Large	Small (minified)
Incremental	Yes	No
Source maps	Full	Limited
Tree shaking	No	Yes
Production ready	No	Yes

Troubleshooting

Module not found errors

If you see module loading errors, ensure all dependencies are properly declared in your pubspec.yaml.

Slow compilation

• Check for circular dependencies
• Reduce the number of entry points
• Use --delete-conflicting-outputs flag

Source maps not working

• Ensure --enable-asserts is not interfering
• Check browser DevTools settings
• Clear browser cache