Example build.yaml. You might also set -O4 instead

build.yaml

targets:
  $default:
    sources:
      - lib/**
      - web/**
      # Note that it is important to include these in the default target.
      - pubspec.*
      - $package$
    builders:
      # -----------------------
      build_web_compilers|entrypoint:
        release_options:
          dart2js_args:
            - --fast-startup
            - -O3