library_prefixes 
            
            Use lowercase_with_underscores when specifying a library prefix.
This rule is available as of Dart 2.0.0.
Rule sets: recommended, flutter
Details
DO use lowercase_with_underscores when specifying a library prefix.
BAD:
import 'dart:math' as Math;
import 'dart:json' as JSON;
import 'package:js/js.dart' as JS;
import 'package:javascript_utils/javascript_utils.dart' as jsUtils;
GOOD:
import 'dart:math' as math;
import 'dart:json' as json;
import 'package:js/js.dart' as js;
import 'package:javascript_utils/javascript_utils.dart' as js_utils;
Usage
To enable the library_prefixes rule,
add library_prefixes under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - library_prefixes