isDev top-level constant

const isDev = const String.fromEnvironment('dss') != 'prod'

Determine if the web is running in production mode or not.

To enable production mode, set an environment variable dss to prod.

build.yaml:

targets:
  $default:
    builders:
      build_web_compilers|entrypoint:
        options:
          compiler: dart2js
          dart2js_args:
          - --fast-startup
          - --minify
          - --trust-type-annotations
          - --trust-primitives
          - -Ddss=prod # This line is needed to enable production mode.

Implementation 

const isDev = const String.fromEnvironment('dss') != 'prod'