Using --define in Dart

You can pass additional --define values to Dart by specifying them in the toolArgs field of your launch configuration (launch.json):

"configurations": [
	{
		"name": "Dart",
		"request": "launch",
		"type": "dart",
		"toolArgs": [
			"--define=MY_VAR=MY_VALUE",
			"--define=MY_OTHER_VAR=MY_OTHER_VALUE"
		]
	}
]

Using the example above, you can print MY_VALUE and MY_OTHER_VALUE by using the String.fromEnvironment constructor:

print(const String.fromEnvironment('MY_VAR'));
print(const String.fromEnvironment('MY_OTHER_VAR'));

For Flutter apps, you should use --dart-define.